https://github.com/NixOS/nix/tree/master/src/nix
https://github.com/NixOS/nix/blob/master/src/nix/main.cc

2018
http://www.opennet.ru/opennews/art.shtml?num=48133

nix
    --version
        ... nix-shell -p nixUnstable
    shell
        nix shell should set IN_NIX_SHELL variable
        https://github.com/NixOS/nix/issues/3862
    develop
        -f file.nix -c $SHELL

$ ls -l ./result/bin/
.r-xr-xr-x 1.8M root  1 Jan  1970 nix
lrwxrwxrwx    3 root  1 Jan  1970 nix-build -> nix
lrwxrwxrwx    3 root  1 Jan  1970 nix-channel -> nix
lrwxrwxrwx    3 root  1 Jan  1970 nix-collect-garbage -> nix
lrwxrwxrwx    3 root  1 Jan  1970 nix-copy-closure -> nix
lrwxrwxrwx    3 root  1 Jan  1970 nix-daemon -> nix
lrwxrwxrwx    3 root  1 Jan  1970 nix-env -> nix
lrwxrwxrwx    3 root  1 Jan  1970 nix-hash -> nix
lrwxrwxrwx    3 root  1 Jan  1970 nix-instantiate -> nix
lrwxrwxrwx    3 root  1 Jan  1970 nix-prefetch-url -> nix
lrwxrwxrwx    3 root  1 Jan  1970 nix-shell -> nix
lrwxrwxrwx    3 root  1 Jan  1970 nix-store -> nix