nix-prefetch-url - Man Page

nix-prefetch-url [--version] [--type hashAlgo] [--print-path] [--unpack] [--name name] url [hash]

The command nix-prefetch-url downloads the file referenced by the URL url, prints its cryptographic hash, and copies it into the Nix store​. The file name in the store is hash-baseName, where baseName is everything following the final slash in url​.

This command is just a convenience for Nix expression writers​. Often a Nix expression fetches some source distribution from the network using the fetchurl expression contained in Nixpkgs​. However, fetchurl requires a cryptographic hash​. If you don't know the hash, you would have to download the file first, and then fetchurl would download it again when you build your Nix expression​. Since fetchurl uses the same name for the downloaded file as nix-prefetch-url, the redundant download can be avoided​.

If hash is specified, then a download is not performed if the Nix store already contains a file with the same hash and base name​. Otherwise, the file is downloaded, and an error is signaled if the actual hash of the file does not match the specified hash​.

This command prints the hash on standard output​. Additionally, if the option --print-path is used, the path of the downloaded file in the Nix store is also printed​.

--type hashAlgo

Use the specified cryptographic hash algorithm, which can be one of md5, sha1, and sha256​.

--print-path

Print the store path of the downloaded file on standard output​.

--unpack

Unpack the archive (which must be a tarball or zip file) and add the result to the Nix store​. The resulting hash can be used with functions such as Nixpkgs’s fetchzip or fetchFromGitHub​.

--name name

Override the name of the file in the Nix store​. By default, this is hash-basename, where basename is the last component of url​. Overriding the name is necessary when basename contains characters that are not allowed in Nix store paths​.

$ nix-prefetch-url ftp://ftp​.gnu​.org/pub/gnu/hello/hello-2​.10​.tar​.gz
0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i

$ nix-prefetch-url --print-path mirror://gnu/hello/hello-2​.10​.tar​.gz
0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i
/nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2​.10​.tar​.gz

$ nix-prefetch-url --unpack --print-path https://github​.com/NixOS/patchelf/archive/0​.8​.tar​.gz
079agjlv0hrv7fxnx9ngipx14gyncbkllxrp9cccnh3a50fxcmy7
/nix/store/19zrmhm3m40xxaw81c8cqm6aljgrnwj2-0​.8​.tar​.gz

Eelco Dolstra

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