Find a fetchurl file in /nix/store?

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1

How do I find a file in the nix store which I have fetchurled in the past?

Here is my situation. I have a specialfile which I downloaded from unreliable.com, but unreliable.com has gone offline. Now I want to save a copy of specialfile. I know specialfile is in my /nix/store because derivations which depend on specialfile still succeed. I aquired specialfile like this:

fetchurl
  { url = "https://unreliable.com/specialfile";
    sha256 = "sha256-EVA7G7f+eP0q3u0oGcD9RpbPIUn83ClrMddCIbyTVK4=";
  };
2

I think nix hash to-nar sha256-EVA7G7f+eP0q3u0oGcD9RpbPIUn83ClrMddCIbyTVK4= would do the trick but that command doesn’t exist?

3

toString on the resulting derivation will give you the path. Assuming specialfile is already in your store you should be able to do something like this:

▶ nix repl
Welcome to Nix 2.7.0. Type :? for help.

nix-repl> builtins.fetchurl {
    url = "https://unreliable.com/specialfile";
    sha256 = "sha256-EVA7G7f+eP0q3u0oGcD9RpbPIUn83ClrMddCIbyTVK4=";
}
"/nix/store/<hash>-specialfile"

nix-repl>
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4

In a cinch, and with a fast enough drive, find /nix/store/ -name '*specialfile*' can also do the trick.

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5

Thanks for the answers but I still can’t find the specialfile. I can see from /nix/store/npxpdhbi6azk4vcmjdqv9mnp8nx2ikz9-specialfile.drv that the "out" path for specialfile should be /nix/store/jlbm1nwc29ibpkxvxm4m2igqj73xh6kn-specialfile, but there is no such file.

I didn’t mention that I never did the fetchurl on this machine; actually someone else did the fetchurl and stored it in a central private cache and I’ve always gotten it from the cache. Does that make a difference? I think it shouldn’t?

6

What was going on here is that the specialfile was in the cache. I had never actually downloaded specialfile from the cache, I had only downloaded cached derivations which depended on specialfile.

Here’s how to query the cache, from @cdepillabout :

nix path-info --json --store https://me.cachix.org/nix/store/jlbm1nwc29ibpkxvxm4m2igqj73xh6kn-specialfile | jq

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