# zenithal @ Sun in ~ [4:38:57]
$ echo $NIX_SHELL_PACKAGES
# zenithal @ Sun in ~ [4:39:04]
$ nix-shell -p mtr
# zenithal @ Sun in ~ [4:39:09] { mtr }
$ echo $NIX_SHELL_PACKAGES
mtr
# zenithal @ Sun in ~ [4:39:13] { mtr }
$ nix-shell -p go
# zenithal @ Sun in ~ [4:39:19] { mtr go }
$ echo $NIX_SHELL_PACKAGES
mtr go
# zenithal @ Sun in ~ [4:39:22] { mtr go }
$ nix-shell -p nodejs
# zenithal @ Sun in ~ [4:39:29] { mtr go nodejs }
$ echo $NIX_SHELL_PACKAGES
mtr go nodejs
Demo: