[.tar.gz` as `from`, or the flake syntax Eelco mentioned [above](https://discourse.nixos.org/t/concept-use-any-package-version/6515/3).
---
]
### Author:  [@davidak](https://discourse.nixos.org/u/davidak)
#### Post date: [April 1, 2020, 12:23pm UTC](https://discourse.nixos.org/t/concept-use-any-package-version/6515/14 "2020-04-01T12:23:44Z")
> [@FRidh](#):
>
> Already exists
>
> ```auto
> nix run -f channel:nixos-20.03 hello
>
> ```
Yes. My goal is to make it simpler and more convenient to use.
`nix run hello@nixos-20.03`
is not only shorter, i think it’s symantically better.
Like you can read it as “Nix, please run the package hello with the version available in NixOS 20.03 release”.
It would share the syntax with specifying a specific version from history or at a specific commit.
`nix run hello@2.8` (search in history index for commit id)
`nix run hello@master` (fetch git master)
`nix run hello@9cc3372` (git commit)
`nix run hello@nixos-20.03` (channel)
---
### Author:  [@edolstra](https://discourse.nixos.org/u/edolstra)
#### Post date: [April 1, 2020, 12:48pm UTC](https://discourse.nixos.org/t/concept-use-any-package-version/6515/15 "2020-04-01T12:48:09Z")
Except for the first example (searching history) the nix-flakes branch supports these:
```auto
nix run nixpkgs/master#hello
nix run nixpkgs/9cc3372#hello
nix run nixpkgs/nixos-20.03#hello
```
---
### Author:  [@volth](https://discourse.nixos.org/u/volth)
#### Post date: [April 1, 2020, 2:06pm UTC](https://discourse.nixos.org/t/concept-use-any-package-version/6515/16 "2020-04-01T14:06:28Z")
`firefox@55` is a perfect example why it won’t work:
1. Moving old derivation into modern (20.03) nixpkgs won’t work because older `firefox`es require patches to be built against glibc 2.30 (people are willing to avoid supporting such patches, that’s why old software disappears from nixpkgs so quickly)
2. Importing `firefox@55` from older nixpkgs together with older glibc, older GTK, … won’t work because there are too many singletons in NixOS GUI (OpenGL, GTK env vars pointing to .so files, …) and here we would get into classical DLL Hell.
---
### Author:  [@davidak](https://discourse.nixos.org/u/davidak)
#### Post date: [April 1, 2020, 2:24pm UTC](https://discourse.nixos.org/t/concept-use-any-package-version/6515/17 "2020-04-01T14:24:36Z")
Yes, might be a bad example. As i said in the Remarks section, only packages work that have no additional dependency on some service or API (the kernel API is quiet stable, right?).
To 1.: glibc is a library, not a running service. why wouldn’t firefox@55 use an old glibc that works? is it not defined as dependency, so the package is impure?
We could add a `meta.portable = false;` (or pure?) to them. But that won’t get into old channels.
A practical exaple: we used a specific version of ansible at my former company, so our shared config works for everyone. It was easy to install it with pip on macOS, but was not straight forward on NixOS.
This feature could be huge in reproducible science. But pinning nixpkgs should be preferred.
We have to document it accordingly, what works, what might work and what is expected to break.
---
### Author:  [@edolstra](https://discourse.nixos.org/u/edolstra)
#### Post date: [April 1, 2020, 3:38pm UTC](https://discourse.nixos.org/t/concept-use-any-package-version/6515/18 "2020-04-01T15:38:57Z")
> [@volth](#):
>
> Importing `firefox@55` from older nixpkgs together with older glibc, older GTK, … won’t work because there are too many singletons in NixOS GUI (OpenGL, GTK env vars pointing to .so files, …) and here we would get into classical DLL Hell.
Well, that’s a separate issue that we really need to address. It used to be that you could fairly reliably use a binary closure between different versions of NixOS or on a different Linux distribution. Nowadays they just tend to segfault.
---
### Author:  [@davidak](https://discourse.nixos.org/u/davidak)
#### Post date: [April 1, 2020, 3:44pm UTC](https://discourse.nixos.org/t/concept-use-any-package-version/6515/19 "2020-04-01T15:44:10Z")
> [@edolstra](#):
>
> Except for the first example (searching history) the nix-flakes branch supports these:
>
> ```auto
> nix run nixpkgs/master#hello
> nix run nixpkgs/9cc3372#hello
> nix run nixpkgs/nixos-20.03#hello
>
> ```
Great, so we talk just about the UI. I think that looks cluttered and # is a strange character to use in a parameter.
What do you think about the @ symantically? like ‘package at version x’ if we use that instead of #, it would look like
`nix run nixpkgs/hello@nixos-20.03`
It still feels cluttered because 3 elements are stitched together and is hard to read. A better symantic would be:
`nix run --from nixpkgs hello@nixos-20.03`
But what if we want a package from another flake in that shell?
`nix run --from nixpkgs hello@nixos-20.03 --from dwarffs dwarffs`
I suggest since years to set nixpkgs as default channel/flake, so we don’t have to set it explicitely in the tools.
`nix run hello@nixos-20.03 --from dwarffs dwarffs`
or just hello
`nix run hello@nixos-20.03`
or just hello from default channel
`nix run hello`
here we finally have a very short and simple command! and this is probably the most common use-case.
and the same syntax can be used for imperative install:
`nix install hello`
or
`nix install hello@nixos-20.03 --from dwarffs dwarffs`
i think that would be quiet intuitive.
---
### Author:  [@edolstra](https://discourse.nixos.org/u/edolstra)
#### Post date: [April 1, 2020, 5:20pm UTC](https://discourse.nixos.org/t/concept-use-any-package-version/6515/20 "2020-04-01T17:20:34Z")
The `#` character comes from URLs. The flake references in the examples above are really abbreviations for a URL like `git+https://github.com/NixOS/nixpkgs.git?ref=master#hello`.
> [@davidak](#):
>
> `nix run hello`
In the flake world, this command runs the default package from the “hello” flake. There is no default channel like nixpkgs (in fact there are no channels anymore).
[Next page](https://discourse.nixos.org/t/concept-use-any-package-version/6515.md?page=2)