View source for FAQ/Why not use nix-env -i foo?

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== Why not use nix-env -i hello? ==

<code>nix-env -i hello</code> is slower and tends to be less precise than <code>nix-env -f '<nixpkgs>' -iA hello</code>. This is because it will evaluate all of nixpkgs searching for packages with the name <code>hello</code>, and install the one [https://nixos.org/nix/manual/#description-1 determined to be the latest] (which may not even be the one that you want). Meanwhile, with <code>-A</code>, nix-env will evaluate only the given attribute in nixpkgs. This will be significantly faster, consume significantly less memory, and more likely get you what you want.

<code>nix-env -u</code> has the same problem, searching for all the packages in the user environment by name and upgrading them. This may lead to unwanted major-version upgrades like JDK 8 → JDK 9. If you want to have a declarative user environment, you may wish to use [[Home Manager]]. It is also possible to home-bake a pure nix solution like [https://gist.github.com/LnL7/570349866bb69467d0caf5cb175faa74 LnL's]. With this setup, you can update your packages by simply running <code>nix-rebuild</code>.</onlyinclude>