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<section xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xi="http://www.w3.org/2001/XInclude"
xml:id="sec-pkgs-fetchers">
<title>Fetcher functions</title>
<para>
When using Nix, you will frequently need to download source code and other
files from the internet. Nixpkgs comes with a few helper functions that allow
you to fetch fixed-output derivations in a structured way.
</para>
<para>
The two fetcher primitives are <function>fetchurl</function> and
<function>fetchzip</function>. Both of these have two required arguments, a
URL and a hash. The hash is typically <literal>sha256</literal>, although
many more hash algorithms are supported. Nixpkgs contributors are currently
recommended to use <literal>sha256</literal>. This hash will be used by Nix
to identify your source. A typical usage of fetchurl is provided below.
</para>
<programlisting><![CDATA[
{ stdenv, fetchurl }:
stdenv.mkDerivation {
name = "hello";
src = fetchurl {
url = "http://www.example.org/hello.tar.gz";
sha256 = "1111111111111111111111111111111111111111111111111111";
};
}
]]></programlisting>
<para>
The main difference between <function>fetchurl</function> and
<function>fetchzip</function> is in how they store the contents.
<function>fetchurl</function> will store the unaltered contents of the URL
within the Nix store. <function>fetchzip</function> on the other hand will
decompress the archive for you, making files and directories directly
accessible in the future. <function>fetchzip</function> can only be used with
archives. Despite the name, <function>fetchzip</function> is not limited to
.zip files and can also be used with any tarball.
</para>
<para>
<function>fetchpatch</function> works very similarly to
<function>fetchurl</function> with the same arguments expected. It expects
patch files as a source and and performs normalization on them before
computing the checksum. For example it will remove comments or other unstable
parts that are sometimes added by version control systems and can change over
time.
</para>
<para>
Other fetcher functions allow you to add source code directly from a VCS such
as subversion or git. These are mostly straightforward names based on the
name of the command used with the VCS system. Because they give you a working
repository, they act most like <function>fetchzip</function>.
</para>
<variablelist>
<varlistentry>
<term>
<literal>fetchsvn</literal>
</term>
<listitem>
<para>
Used with Subversion. Expects <literal>url</literal> to a Subversion
directory, <literal>rev</literal>, and <literal>sha256</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>fetchgit</literal>
</term>
<listitem>
<para>
Used with Git. Expects <literal>url</literal> to a Git repo,
<literal>rev</literal>, and <literal>sha256</literal>.
<literal>rev</literal> in this case can be full the git commit id (SHA1
hash) or a tag name like <literal>refs/tags/v1.0</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>fetchfossil</literal>
</term>
<listitem>
<para>
Used with Fossil. Expects <literal>url</literal> to a Fossil archive,
<literal>rev</literal>, and <literal>sha256</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>fetchcvs</literal>
</term>
<listitem>
<para>
Used with CVS. Expects <literal>cvsRoot</literal>, <literal>tag</literal>,
and <literal>sha256</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>fetchhg</literal>
</term>
<listitem>
<para>
Used with Mercurial. Expects <literal>url</literal>,
<literal>rev</literal>, and <literal>sha256</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
A number of fetcher functions wrap part of <function>fetchurl</function> and
<function>fetchzip</function>. They are mainly convenience functions intended
for commonly used destinations of source code in Nixpkgs. These wrapper
fetchers are listed below.
</para>
<variablelist>
<varlistentry>
<term>
<literal>fetchFromGitHub</literal>
</term>
<listitem>
<para>
<function>fetchFromGitHub</function> expects four arguments.
<literal>owner</literal> is a string corresponding to the GitHub user or
organization that controls this repository. <literal>repo</literal>
corresponds to the name of the software repository. These are located at
the top of every GitHub HTML page as
<literal>owner</literal>/<literal>repo</literal>. <literal>rev</literal>
corresponds to the Git commit hash or tag (e.g <literal>v1.0</literal>)
that will be downloaded from Git. Finally, <literal>sha256</literal>
corresponds to the hash of the extracted directory. Again, other hash
algorithms are also available but <literal>sha256</literal> is currently
preferred.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>fetchFromGitLab</literal>
</term>
<listitem>
<para>
This is used with GitLab repositories. The arguments expected are very
similar to fetchFromGitHub above.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>fetchFromBitbucket</literal>
</term>
<listitem>
<para>
This is used with BitBucket repositories. The arguments expected are very
similar to fetchFromGitHub above.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>fetchFromSavannah</literal>
</term>
<listitem>
<para>
This is used with Savannah repositories. The arguments expected are very
similar to fetchFromGitHub above.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>fetchFromRepoOrCz</literal>
</term>
<listitem>
<para>
This is used with repo.or.cz repositories. The arguments expected are very
similar to fetchFromGitHub above.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
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