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Fetchers
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.
The two fetcher primitives are fetchurl
and fetchzip
. Both of these have two required arguments, a URL and a hash. The hash is typically sha256
, although many more hash algorithms are supported. Nixpkgs contributors are currently recommended to use sha256
. This hash will be used by Nix to identify your source. A typical usage of fetchurl is provided below.
{ stdenv, fetchurl }:
stdenv.mkDerivation {
name = "hello";
src = fetchurl {
url = "http://www.example.org/hello.tar.gz";
sha256 = "1111111111111111111111111111111111111111111111111111";
};
}
The main difference between fetchurl
and fetchzip
is in how they store the contents. fetchurl
will store the unaltered contents of the URL within the Nix store. fetchzip
on the other hand will decompress the archive for you, making files and directories directly accessible in the future. fetchzip
can only be used with archives. Despite the name, fetchzip
is not limited to .zip files and can also be used with any tarball.
fetchpatch
works very similarly to fetchurl
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.
Other fetcher functions allow you to add source code directly from a VCS such as subversion or git. These are mostly straightforward nambes based on the name of the command used with the VCS system. Because they give you a working repository, they act most like fetchzip
.
fetchsvn
Used with Subversion. Expects url
to a Subversion directory, rev
, and sha256
.
fetchgit
Used with Git. Expects url
to a Git repo, rev
, and sha256
. rev
in this case can be full the git commit id (SHA1 hash) or a tag name like refs/tags/v1.0
.
fetchfossil
Used with Fossil. Expects url
to a Fossil archive, rev
, and sha256
.
fetchcvs
Used with CVS. Expects cvsRoot
, tag
, and sha256
.
fetchhg
Used with Mercurial. Expects url
, rev
, and sha256
.
A number of fetcher functions wrap part of fetchurl
and fetchzip
. They are mainly convenience functions intended for commonly used destinations of source code in Nixpkgs. These wrapper fetchers are listed below.
fetchFromGitHub
fetchFromGitHub
expects four arguments. owner
is a string corresponding to the GitHub user or organization that controls this repository. repo
corresponds to the name of the software repository. These are located at the top of every GitHub HTML page as owner
/repo
. rev
corresponds to the Git commit hash or tag (e.g v1.0
) that will be downloaded from Git. Finally, sha256
corresponds to the hash of the extracted directory. Again, other hash algorithms are also available but sha256
is currently preferred.
fetchFromGitLab
This is used with GitLab repositories. The arguments expected are very similar to fetchFromGitHub above.
fetchFromGitiles
This is used with Gitiles repositories. The arguments expected are similar to fetchgit.
fetchFromBitbucket
This is used with BitBucket repositories. The arguments expected are very similar to fetchFromGitHub above.
fetchFromSavannah
This is used with Savannah repositories. The arguments expected are very similar to fetchFromGitHub above.
fetchFromRepoOrCz
This is used with repo.or.cz repositories. The arguments expected are very similar to fetchFromGitHub above.