nix-env -qa not showing latest packages - nix

Question

I tried to update nix-env but it is not showing latest packages:
a_user[~]$ nix-channel --update
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LANGUAGE = "en_US",
LC_ALL = "en_US",
LC_COLLATE = "C",
LANG = "en_US"
are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
downloading Nix expressions from âhttps://nixos.org/releases/nixpkgs/nixpkgs-16.03pre71923.3087ef3//nixexprs.tar.xzâ...
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LANGUAGE = "en_US",
LC_ALL = "en_US",
LC_COLLATE = "C",
LANG = "en_US"
are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0
unpacking channels...
a_user[~]$
a_user[~]$
a_user[~]$ nix-env -qa | grep baobab
baobab-3.16.1
a_user[~]$
a_user[~]$
a_user[~]$ nix-env -qa | grep dicom
a_user[~]$
a_user[~]$
a_user[~]$ nix-env -qa | grep grassroot
a_user[~]$
a_user[~]$
grassroot-dicom is available: https://github.com/NixOS/nixpkgs/search?utf8=%E2%9C%93&q=dicom
Also, baobab version 3.18 is available: https://github.com/NixOS/nixpkgs/search?utf8=%E2%9C%93&q=baobab
Why this discrepancy and how can I resolve this?
Also, how to correct locale settings in Slackware? Thanks.

Answer 1

Your search result for "dicom" found that string in the description of a package, alright, but that package is not called "dicom": it's called gdcm. You can do a similar search with nix-env as follows:
nix-env -qaP --description | grep -i dicom
gdcm gdcm-2.4.4 The grassroots cross-platform DICOM implementation
The output has three columns. The first one is the attribute path to the package, which you can use to install the package with nix-env -iA. The second column shows the package's name, which you can use to install it with nix-env -i. The third column is the short description of the package, which has no relevant inside of Nix; it's intended just for humans.
Now, to install the package, run nix-env -i gdcm or nix-env -iA gdcm. Both commands will work, but the latter one (the one using the attribute path) is usually faster.
The package baobab-3.18.0 is available in the master branch of the Nixpkgs git repository, but it's not yet available in the nixos-unstable channel. The channel hasn't advanced to the latest version of master yet, because there are regression test failures that need to be fixed before the channel is updated. The new version of baobab will show up in the channel in a couple of days (state of 2015-11-26). Simply put, the channel updates every time an entire column in the build set https://hydra.nixos.org/job/nixos/trunk-combined/tested#tabs-constituents is green, and this hasn't happened in a while: https://github.com/NixOS/nixpkgs/issues/11097 has more details.