<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> <prompt>$ </prompt>git clone https://github.com/NixOS/nixpkgs <prompt>$ </prompt>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> <prompt>$ </prompt>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> <prompt>$ </prompt>emacs pkgs/development/libraries/libfoo/default.nix <prompt>$ </prompt>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> <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> <prompt>$ </prompt>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> <prompt>$ </prompt>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> <prompt>$ </prompt>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>