<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xml:id="chap-quick-start">
<title>Quick Start to Adding a Package</title>
<para>
To add a package to Nixpkgs:
<orderedlist>
<listitem>
<para>
Checkout the Nixpkgs source tree:
<screen>
$ git clone git://github.com/NixOS/nixpkgs.git
$ cd nixpkgs</screen>
</para>
</listitem>
<listitem>
<para>
Find a good place in the Nixpkgs tree to add the Nix expression for your
package. For instance, a library package typically goes into
<filename>pkgs/development/libraries/<replaceable>pkgname</replaceable></filename>,
while a web browser goes into
<filename>pkgs/applications/networking/browsers/<replaceable>pkgname</replaceable></filename>.
See <xref linkend="sec-organisation" /> for some hints on the tree
organisation. Create a directory for your package, e.g.
<screen>
$ mkdir pkgs/development/libraries/libfoo</screen>
</para>
</listitem>
<listitem>
<para>
In the package directory, create a Nix expression — a piece of code that
describes how to build the package. In this case, it should be a
<emphasis>function</emphasis> that is called with the package dependencies
as arguments, and returns a build of the package in the Nix store. The
expression should usually be called <filename>default.nix</filename>.
<screen>
$ emacs pkgs/development/libraries/libfoo/default.nix
$ git add pkgs/development/libraries/libfoo/default.nix</screen>
</para>
<para>
You can have a look at the existing Nix expressions under
<filename>pkgs/</filename> to see how it’s done. Here are some good
ones:
<itemizedlist>
<listitem>
<para>
GNU Hello:
<link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/misc/hello/default.nix"><filename>pkgs/applications/misc/hello/default.nix</filename></link>.
Trivial package, which specifies some <varname>meta</varname>
attributes which is good practice.
</para>
</listitem>
<listitem>
<para>
GNU cpio:
<link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/tools/archivers/cpio/default.nix"><filename>pkgs/tools/archivers/cpio/default.nix</filename></link>.
Also a simple package. The generic builder in <varname>stdenv</varname>
does everything for you. It has no dependencies beyond
<varname>stdenv</varname>.
</para>
</listitem>
<listitem>
<para>
GNU Multiple Precision arithmetic library (GMP):
<link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/libraries/gmp/5.1.x.nix"><filename>pkgs/development/libraries/gmp/5.1.x.nix</filename></link>.
Also done by the generic builder, but has a dependency on
<varname>m4</varname>.
</para>
</listitem>
<listitem>
<para>
Pan, a GTK-based newsreader:
<link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/networking/newsreaders/pan/default.nix"><filename>pkgs/applications/networking/newsreaders/pan/default.nix</filename></link>.
Has an optional dependency on <varname>gtkspell</varname>, which is
only built if <varname>spellCheck</varname> is <literal>true</literal>.
</para>
</listitem>
<listitem>
<para>
Apache HTTPD:
<link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/servers/http/apache-httpd/2.4.nix"><filename>pkgs/servers/http/apache-httpd/2.4.nix</filename></link>.
A bunch of optional features, variable substitutions in the configure
flags, a post-install hook, and miscellaneous hackery.
</para>
</listitem>
<listitem>
<para>
Thunderbird:
<link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/networking/mailreaders/thunderbird/default.nix"><filename>pkgs/applications/networking/mailreaders/thunderbird/default.nix</filename></link>.
Lots of dependencies.
</para>
</listitem>
<listitem>
<para>
JDiskReport, a Java utility:
<link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/tools/misc/jdiskreport/default.nix"><filename>pkgs/tools/misc/jdiskreport/default.nix</filename></link>
(and the
<link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/tools/misc/jdiskreport/builder.sh">builder</link>).
Nixpkgs doesn’t have a decent <varname>stdenv</varname> for Java yet
so this is pretty ad-hoc.
</para>
</listitem>
<listitem>
<para>
XML::Simple, a Perl module:
<link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/top-level/perl-packages.nix"><filename>pkgs/top-level/perl-packages.nix</filename></link>
(search for the <varname>XMLSimple</varname> attribute). Most Perl
modules are so simple to build that they are defined directly in
<filename>perl-packages.nix</filename>; no need to make a separate file
for them.
</para>
</listitem>
<listitem>
<para>
Adobe Reader:
<link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/misc/adobe-reader/default.nix"><filename>pkgs/applications/misc/adobe-reader/default.nix</filename></link>.
Shows how binary-only packages can be supported. In particular the
<link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/misc/adobe-reader/builder.sh">builder</link>
uses <command>patchelf</command> to set the RUNPATH and ELF interpreter
of the executables so that the right libraries are found at runtime.
</para>
</listitem>
</itemizedlist>
</para>
<para>
Some notes:
<itemizedlist>
<listitem>
<para>
All <varname linkend="chap-meta">meta</varname> attributes are
optional, but it’s still a good idea to provide at least the
<varname>description</varname>, <varname>homepage</varname> and
<varname
linkend="sec-meta-license">license</varname>.
</para>
</listitem>
<listitem>
<para>
You can use <command>nix-prefetch-url</command> (or similar
nix-prefetch-git, etc) <replaceable>url</replaceable> to get the
SHA-256 hash of source distributions. There are similar commands as
<command>nix-prefetch-git</command> and
<command>nix-prefetch-hg</command> available in
<literal>nix-prefetch-scripts</literal> package.
</para>
</listitem>
<listitem>
<para>
A list of schemes for <literal>mirror://</literal> URLs can be found in
<link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/build-support/fetchurl/mirrors.nix"><filename>pkgs/build-support/fetchurl/mirrors.nix</filename></link>.
</para>
</listitem>
</itemizedlist>
</para>
<para>
The exact syntax and semantics of the Nix expression language, including
the built-in function, are described in the Nix manual in the
<link
xlink:href="http://hydra.nixos.org/job/nix/trunk/tarball/latest/download-by-type/doc/manual/#chap-writing-nix-expressions">chapter
on writing Nix expressions</link>.
</para>
</listitem>
<listitem>
<para>
Add a call to the function defined in the previous step to
<link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/top-level/all-packages.nix"><filename>pkgs/top-level/all-packages.nix</filename></link>
with some descriptive name for the variable, e.g.
<varname>libfoo</varname>.
<screen>
$ emacs pkgs/top-level/all-packages.nix</screen>
</para>
<para>
The attributes in that file are sorted by category (like “Development /
Libraries”) that more-or-less correspond to the directory structure of
Nixpkgs, and then by attribute name.
</para>
</listitem>
<listitem>
<para>
To test whether the package builds, run the following command from the
root of the nixpkgs source tree:
<screen>
$ nix-build -A libfoo</screen>
where <varname>libfoo</varname> should be the variable name defined in the
previous step. You may want to add the flag <option>-K</option> to keep
the temporary build directory in case something fails. If the build
succeeds, a symlink <filename>./result</filename> to the package in the
Nix store is created.
</para>
</listitem>
<listitem>
<para>
If you want to install the package into your profile (optional), do
<screen>
$ nix-env -f . -iA libfoo</screen>
</para>
</listitem>
<listitem>
<para>
Optionally commit the new package and open a pull request, or send a patch
to <literal>https://groups.google.com/forum/#!forum/nix-devel</literal>.
</para>
</listitem>
</orderedlist>
</para>
</chapter>