Minimal example: export v824=$(nix-build 'channel:nixos-15.09-small' -A coreutils) export v830=$(nix-build 'channel:nixos-19.09-small' -A coreutils) $v82

Minimal example: export v824=$(nix-build 'channel:nixos-15.09-small' -A coreutils) export v830=$(nix-build 'channel:nixos-19.09-small' -A coreutils) $v824/bin/cat /etc/passwd | $v830/bin/cat -A You can get better specificity by using a nixpkgs git repo/hash instead of channel or adding `--no-out-link`, but this is minimal.