# Concept: use any package version
**URL:** https://discourse.nixos.org/t/concept-use-any-package-version/6515
**Category:** Development
**Created:** [April 1, 2020, 1:47am UTC](https://discourse.nixos.org/t/concept-use-any-package-version/6515 "2020-04-01T01:47:40Z")
**Posts on this page:** 1
**Showing post:** 3
### Author:  [@edolstra](https://discourse.nixos.org/u/edolstra)
#### Post date: [April 1, 2020, 7:56am UTC](https://discourse.nixos.org/t/concept-use-any-package-version/6515/3 "2020-04-01T07:56:59Z")
With flakes it’s already pretty easy to run/install something from an arbitrary version of Nixpkgs, e.g.
```auto
$ nix run nixpkgs/9077284a7ca32efd56e652286fdaa2ad851ce0c9#hello -c hello
Hello, world!
```
What is missing is a way to search historical versions of Nixpkgs for a particular version of a package. This cannot be done locally because it would be way too expensive and the database would be too large. However, @garbas is working on loading the `packages.json` files from each Nixpkgs release into ElasticSearch. The capability to search this database could be added to the `nix` CLI as a convenience.
However this would only be a CLI thing. This:
> `environment.systemPackages = with pkgs; [firefox@55];`
will never work because `firefox@55` is very under-specified: Nix would have no idea what `firefox@55` to use. Also, we’re moving away from a reliance on version numbers. The `nix` command, unlike `nix-env`, is based on attribute names rather than `-`.
> This can be build by a standalone hydra job from master branch.
That’s basically [https://hydra.nixos.org/job/nixpkgs/trunk/tarball/latest/download-by-type/file/json-br](https://hydra.nixos.org/job/nixpkgs/trunk/tarball/latest/download-by-type/file/json-br).
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