[Nix-dev] weird garbage output inside nix-shell

[Linus]

>> I kind of thought I shouldn't even be able to launch vim from inside
>> my shell if it's not listed as a buildDep.
>
>It looks to me that nix-shell _extends_ the environment it is run in.
>So, if you run nix-shell in an environment which contains vim, you have
>vim inside nix-shell.

Correct — unless you use the --pure option in which case the environment is cleared before adding the build inputs.