nix-prefetch-url

1

Nix

nix-prefetch-url

copy a file from a URL into the store and print its hash

nix-prefetch-url

\--version

\--type

hashAlgo

\--print-path

\--unpack

\--name

name

url

hash

# Description

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.

# Options

  - `--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.

# Examples

    $ 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