nixpkgs/doc/languages-frameworks/pkg-config.section.md

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# pkg-config {#sec-pkg-config}
*pkg-config* is a unified interface for declaring and querying built C/C++ libraries.
Nixpkgs provides a couple of facilities for working with this tool.
## Writing packages providing pkg-config modules {#pkg-config-writing-packages}
Packages should set `meta.pkgConfigModules` with the list of package config modules they provide.
They should also use `testers.testMetaPkgConfig` to check that the final built package matches that list.
Additionally, the [`validatePkgConfig` setup hook](https://nixos.org/manual/nixpkgs/stable/#validatepkgconfig), will do extra checks on to-be-installed pkg-config modules.
A good example of all these things is zlib:
```
{ pkg-config, testers, ... }:
stdenv.mkDerivation (finalAttrs: {
...
nativeBuildInputs = [ pkg-config validatePkgConfig ];
passthru.tests.pkg-config = testers.testMetaPkgConfig finalAttrs.finalPackage;
meta = {
...
pkgConfigModules = [ "zlib" ];
};
})
```
## Accessing packages via pkg-config module name {#sec-pkg-config-usage}
### Within Nixpkgs {#sec-pkg-config-usage-internal}
A [setup hook](#setup-hook-pkg-config) is bundled in the `pkg-config` package to bring a derivation's declared build inputs into the environment.
This will populate environment variables like `PKG_CONFIG_PATH`, `PKG_CONFIG_PATH_FOR_BUILD`, and `PKG_CONFIG_PATH_HOST` based on:
- how `pkg-config` itself is depended upon
- how other dependencies are depended upon
For more details see the section on [specifying dependencies in general](#ssec-stdenv-dependencies).
Normal pkg-config commands to look up dependencies by name will then work with those environment variables defined by the hook.
### Externally {#sec-pkg-config-usage-external}
The `defaultPkgConfigPackages` package set is a set of aliases, named after the modules they provide.
This is meant to be used by language-to-nix integrations.
Hand-written packages should use the normal Nixpkgs attribute name instead.