:::{.example #ex-fetchers-fetchurl-nixpkgs-version}
# Using `fetchurl` to download a file

The following package downloads a small file from a URL and shows the most common way to use `fetchurl`:

```nix
{ fetchurl }:
fetchurl {
  url = "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/.version";
  hash = "sha256-BZqI7r0MNP29yGH5+yW2tjU9OOpOCEvwWKrWCv5CQ0I=";
}
```

After building the package, the file will be downloaded and place into the Nix store:

```shell
$ nix-build
(output removed for clarity)
/nix/store/4g9y3x851wqrvim4zcz5x2v3zivmsq8n-version

$ cat /nix/store/4g9y3x851wqrvim4zcz5x2v3zivmsq8n-version
23.11
```
:::

:::{.example #ex-fetchers-fetchurl-nixpkgs-version-multiple-urls}
# Using `fetchurl` to download a file with multiple possible URLs

The following package adapts [](#ex-fetchers-fetchurl-nixpkgs-version) to use multiple URLs.
The first URL was crafted to intentionally return an error to illustrate how `fetchurl` will try multiple URLs until it finds one that works (or all URLs fail).

```nix
{ fetchurl }:
fetchurl {
  urls = [
    "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/does-not-exist"
    "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/.version"
  ];
  hash = "sha256-BZqI7r0MNP29yGH5+yW2tjU9OOpOCEvwWKrWCv5CQ0I=";
}
```

After building the package, both URLs will be used to download the file:

```shell
$ nix-build
(some output removed for clarity)
trying https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/does-not-exist
(some output removed for clarity)
curl: (22) The requested URL returned error: 404

trying https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/.version
(some output removed for clarity)
/nix/store/n9asny31z32q7sdw6a8r1gllrsfy53kl-does-not-exist

$ cat /nix/store/n9asny31z32q7sdw6a8r1gllrsfy53kl-does-not-exist
23.11
```

However, note that the name of the file was derived from the first URL (this is further explained in [the `fetchurl` overview](#sec-pkgs-fetchers-fetchurl)).
To ensure the result will have the same name regardless of which URLs are used, we can modify the package:

```nix
{ fetchurl }:
fetchurl {
  name = "nixpkgs-version";
  urls = [
    "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/does-not-exist"
    "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/.version"
  ];
  hash = "sha256-BZqI7r0MNP29yGH5+yW2tjU9OOpOCEvwWKrWCv5CQ0I=";
}
```

After building the package, the result will have the name we specified:

```shell
$ nix-build
(output removed for clarity)
/nix/store/zczb6wl3al6jm9sm5h3pr6nqn0i5ji9z-nixpkgs-version
```
:::

:::{.example #ex-fetchers-fetchurl-nixpkgs-version-postfetch}
# Manipulating the content downloaded by `fetchurl`

It might be useful to manipulate the content downloaded by `fetchurl` directly in its derivation.
In this example, we'll adapt [](#ex-fetchers-fetchurl-nixpkgs-version) to append the result of running the `hello` package to the contents we download, purely to illustrate how to manipulate the content.

```nix
{
  fetchurl,
  hello,
  lib,
}:
fetchurl {
  url = "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/.version";

  nativeBuildInputs = [ hello ];

  downloadToTemp = true;
  postFetch = ''
    ${lib.getExe hello} >> $downloadedFile
    mv $downloadedFile $out
  '';

  hash = "sha256-ceooQQYmDx5+0nfg40uU3NNI2yKrixP7HZ/xLZUNv+w=";
}
```

After building the package, the resulting file will have "Hello, world!" appended to it:

```shell
$ nix-build
(output removed for clarity)
/nix/store/ifi6pp7q0ag5h7c5v9h1c1c7bhd10c7f-version

$ cat /nix/store/ifi6pp7q0ag5h7c5v9h1c1c7bhd10c7f-version
23.11
Hello, world!
```

Note that the `hash` specified in the package is different than the hash specified in [](#ex-fetchers-fetchurl-nixpkgs-version), because the contents of the output have changed (even though the actual file that was downloaded is the same).
See [](#chap-pkgs-fetchers-caveats) for more details on how to work with the `hash` attribute when the output changes.
:::

## `fetchzip` {#sec-pkgs-fetchers-fetchzip}