the symlink ~/.nix-userenv to the given argument (which defaults to
.../links/current). /etc/profile.d/nix-profile creates this symlink
if it doesn't exist yet. Example use:
$ nix-env -l my_profile -i foo.nix subversion quake
$ nix-env -p my_profile
I don't like the term "profile". Let's deprecate it :-)