# Packages
Similar to [modules](./modules.md), the pkgs directory mirrors the upstream
[nixpkgs/pkgs][pkgs], and for the same reason; if you ever want to upstream
your package, it's as simple as dropping it into the nixpkgs/pkgs directory.

The only minor difference is that, instead of adding the `callPackage` call to
`all-packages.nix`, you just add it the the _default.nix_ in this directory,
which is defined as a simple overlay.

All the packages are exported via `packages.<system>.<pkg-name>`, for all
the supported systems listed in the package's `meta.platforms` attribute.

And, as usual, every package in the overlay is also available to any NixOS
[host](../concepts/hosts.md).

## Example
pkgs/development/libraries/libinih/default.nix:
```nix
{ stdenv, meson, ninja, lib, srcs, ... }:
let inherit (srcs) libinih; in
stdenv.mkDerivation {
  pname = "libinih";

  # version will resolve to 53, as specified in the final example below
  inherit (libinih) version;

  src = libinih;

  buildInputs = [ meson ninja ];

  # ...
}
```

pkgs/default.nix:
```nix
final: prev: {
  libinih = prev.callPackage ./development/libraries/libinih { };
}
```

pkgs/flake.nix:
```nix
{
  description = "Package sources";

  inputs = {
    libinih.url = "github:benhoyt/inih/r53";
    libinih.flake = false;
  };
}
```

[pkgs]: https://github.com/NixOS/nixpkgs/tree/master/pkgs