Suppose I search for a package to install using nix-env's --query operation:

$ nix-env -qa 'aspell.*en'

I write this package name in /etc/nixos/configuration.nix, NixOS's main configuration file:

environment.systemPackages = with pkgs; [

Yet if I run sudo nixos-rebuild switch, NixOS command to update the configuration and install all system-wide packages specified by declaratively, it aborts with an error:

error: undefined variable ‘aspell-dict-en’ at /etc/nixos/configuration.nix:44:5

I know that for many packages, although not all, the name that nix-env returns and the name one should specify in environment.systemPackages configuration option are different, but I don't understand the logic. How do I install a package that I found through nix-env?

5 Answers 5


NixOS community has three manuals, always consult them first, if you're stuck:

Every package on Nix is specified by a Nix expression. A Nix expression is some text, written in Nix language, typically residing in a file with extension .nix.

Every expression has the so-called “symbolic name”, a human-readable name that is printed, when you use nix-env. See sample Nix expression. Nix itself doesn't use this symbolic name anywhere internally, so it doesn't matter if your package is named aspell-dict-en, it's just for your, human's, convenience.

What actually matters is the so-called “attribute path”. So your confusion is between symbolic name and attribute path. Every package has an attribute path, which you can use in environment.systemPackages configuration option to install system-wide using declarative package management.

To find out your package's attribute path, add another flag -P to your query:

$ nix-env -qaP 'aspell.*en'
nixos.aspellDicts.en  aspell-dict-en-7.1-0

You should be comfortable using nix-env on a daily basis, so practice calling nix-env with --query and --install options. However you can also browse packages and find out their attribute paths online on Nix packages search. Type aspell, click on aspell-dict-en and you'll see various package's properties, including attribute path as part of the install command:

$ nix-env -iA nixos.pkgs.aspellDicts.en

Now you can put this attribute path into /etc/nixos/configuration.nix:

environment.systemPackages = with pkgs; [

Then update the system by running sudo nixos-rebuild switch.

  • 6
    Unfortunately, the -P option does not work with --installed, as can be seen with nix-env -q --installed -P | grep terminus which prints terminus-font instead of terminus_font. The workaround is to use nix-env -qaP | grep terminus-font, but it means that you can't easily dump the output of nix-env -q --installed into the configuration.nix. Oct 14, 2016 at 14:19

In case you are using NixOS for Data Science:

Python modules:

nix-env -qaP .\*pylint.\*


nix-env -qaP | grep -i python36 > ${py_pkgs}
grep pandas ${py_pkgs}

OR if your are searching especially for R packages/libraries

nix-env -f "<nixpkgs>" -qaP -A rPackages .\*tidyverse.\*

alternatively you get e.g. npm packages with:

nix-env -qaPA 'nixos.nodePackages'

there is also a website for searching for pkgs

nix-env -v -qaP '*' | grep "nvim"

I would save the result of nix-env -v -qaP '*' to a file (as it usually takes a while to return).

Bear in mind, nix-env seems to ignore things under haskellPackages (and possibly others). You can search for packages in subcategories such as haskellPackages via nix-env -f '<nixpkgs>' -qaPA haskellPackages

nix-env search is currently quite frustrating as it'll take 5+ seconds and then come back with a error: regex error...


Additional to Mirzhans options: you could check /nix/store like grep -irw "programm-name" /nix/store. But this could be a bit confusing. Also in your home directory you could check the directory .local/share for installed programms/apps.

nix-search () {
    local cache_file=~/.cache/nix/nix-env-qaP

    if [[ "$1" =~ ^--?c(ache)?$ ]]; then
        mkdir -p $(dirname $cache_file)
        echo -n "Caching packages.."
        nix-env -qaP '*' >$cache_file
        echo " 🏁"
        grep -iE "$1" $cache_file
$ nix-search --cache
Caching packages.. 🏁

$ nix-search nodejs
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