NixOS/nix — pull request #271 by soenkehahn (2014-06-03 08:14:13+00:00)
Title: nix-shell adds an environment variable for the used nix files

In shells entered through nix-shell NIX_SHELL_EXPRESSIONS will be set to
the nix files given to the nix-shell command.

The primary motivation for this is to allow for informative prompts in
shells created through nix-shell.