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<chapter xmlns= "http://docbook.org/ns/docbook"
xmlns:xlink= "http://www.w3.org/1999/xlink"
xml:id= "chap-overvie" >
<title > Quick Start to Adding a Package</title>
<para > To add a package to Nixpkgs:
<orderedlist >
<listitem >
<para > Checkout the Nixpkgs source tree:
<screen >
$ svn checkout https://svn.nixos.org/repos/nix/nixpkgs/trunk nixpkgs
$ 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 Section XXX for some hints on the tree organisation. Create a
directory for your package, e.g.
<screen >
$ svn 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
$ svn 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’
good ones:
<itemizedlist >
<listitem >
<para > GNU cpio: <link
xlink:href= "https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/tools/archivers/cpio/default.nix" > <filename > pkgs/tools/archivers/cpio/default.nix</filename> </link> .
The simplest possible 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 Hello: <link
xlink:href= "https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/applications/misc/hello/ex-2/default.nix" > <filename > pkgs/applications/misc/hello/ex-2/default.nix</filename> </link> .
Also trivial, but it specifies some <varname > meta</varname>
attributes which is good practice.</para>
</listitem>
<listitem >
<para > GNU Multiple Precision arithmetic library (GMP): <link
xlink:href= "https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/development/libraries/gmp/default.nix" > <filename > pkgs/development/libraries/gmp/default.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://svn.nixos.org/repos/nix/nixpkgs/trunk/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://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/servers/http/apache-httpd/default.nix" > <filename > pkgs/servers/http/apache-httpd/default.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 > BitTorrent (wxPython-based): <link
xlink:href= "https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/tools/networking/p2p/bittorrent/default.nix" > <filename > pkgs/tools/networking/p2p/bittorrent/default.nix</filename> </link> .
Uses an external <link
xlink:href= "https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/tools/networking/p2p/bittorrent/builder.sh" > build
script</link> , which can be useful if you have lots of code
that you don’
external builders are mostly obsolete.
</para>
</listitem>
<listitem >
<para > Firefox: <link
xlink:href= "https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/applications/networking/browsers/firefox-3/default.nix" > <filename > pkgs/applications/networking/browsers/firefox-3/default.nix</filename> </link> .
Lots of dependencies.</para>
</listitem>
<listitem >
<para > JDiskReport, a Java utility: <link
xlink:href= "https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/tools/misc/jdiskreport/default.nix" > <filename > pkgs/tools/misc/jdiskreport/default.nix</filename> </link>
(and the <link
xlink:href= "https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/tools/misc/jdiskreport/builder.sh" > builder</link> ).
Nixpkgs doesn’ <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://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/top-level/all-packages.nix" > <filename > pkgs/top-level/all-packages.nix</filename> </link>
(search for the <varname > perlXMLSimple</varname>
attribute). Most Perl modules are so simple to build that
they are defined directly in
<filename > all-packages.nix</filename> , no need to make a
separate file for them.</para>
</listitem>
<listitem >
<para > Adobe Reader: <link
xlink:href= "https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/applications/misc/acrobat-reader/default.nix" > <filename > pkgs/applications/misc/acrobat-reader/default.nix</filename> </link> .
Shows how binary-only packages can be supported. In
particular the <link
xlink:href= "https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/applications/misc/acrobat-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 > meta</varname> attributes are optional,
but it’
<varname > description</varname> and
<varname > homepage</varname> .</para>
</listitem>
<listitem >
<para > You can use <command > nix-prefetch-url</command>
<replaceable > url</replaceable> to get the SHA-256 hash of
source distributions.</para>
</listitem>
<listitem >
<para > A list of schemes for <literal > mirror://</literal>
URLs can be found in <link
xlink:href= "https://svn.nixos.org/repos/nix/nixpkgs/trunk/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://nixos.org/releases/nix/unstable/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://svn.nixos.org/repos/nix/nixpkgs/trunk/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 > Test whether the package builds:
<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 (<command > svn
ci</command> ) or send a patch to
<literal > nix-dev@cs.uu.nl</literal> .</para>
</listitem>
<listitem >
<para > If you want the TU Delft build farm to build binaries of the
package and make them available in the <link
xlink:href= "http://nixos.org/releases/nixpkgs/channels/nixpkgs-unstable/" > <literal > nixpkgs</literal>
channel</link> , add it to <link
xlink:href= "https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/top-level/build-for-release.nix" > <filename > pkgs/top-level/build-for-release.nix</filename> </link> .</para>
</listitem>
</orderedlist>
</para>
</chapter>
Eelco Dolstra