[Nix-dev] Temporarily not using ~/.nixpkgs/config.nix

[Eike]

Hello,

I ocassionally search packages from previous nixos versions using for
example this command:

    nix-env -f https://github.com/NixOS/nixpkgs-channels/archive/nixos-16.09.tar.gz -qaP |grep linuxPackages

But often that won't work, because my ~/.nixpkgs/config.nix refers to my
customized package set which is setup for the current unstable channel
and so it might not work with nixos-16.09. I then quickly move
~/.nixpkgs away, run the command and move it back.

Is there a way to temporarily disable evaluating ~/.nixpkgs/config.nix?
I looked at http://nixos.org/nixpkgs/manual/#chap-packageconfig, but
couldn't find anything related.

TIA!
-Eike


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