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# Release 1.6 (2013-09-10)

In addition to the usual bug fixes, this release has several new features:

- The command `nix-build --run-env` has been renamed to `nix-shell`.

- `nix-shell` now sources `$stdenv/setup` inside the interactive shell, rather than in a parent shell. This ensures that shell functions defined by `stdenv` can be used in the interactive shell.

- `nix-shell` has a new flag `--pure` to clear the environment, so you get an environment that more closely corresponds to the “real” Nix build.

- `nix-shell` now sets the shell prompt (`PS1`) to ensure that Nix shells are distinguishable from your regular shells.

- `nix-env` no longer requires a `*` argument to match all packages, so `nix-env -qa` is equivalent to `nix-env -qa '*'`.

- `nix-env -i` has a new flag `--remove-all` (`-r`) to remove all previous packages from the profile. This makes it easier to do declarative package management similar to NixOS’s `environment.systemPackages`. For instance, if you have a specification `my-packages.nix` like this:

      with import <nixpkgs> {};
      [ thunderbird
        geeqie
        ...
      ]

  then after any change to this file, you can run:

      $ nix-env -f my-packages.nix -ir

  to update your profile to match the specification.

- The ‘`with`’ language construct is now more lazy. It only evaluates its argument if a variable might actually refer to an attribute in the argument. For instance, this now works:

      let
        pkgs = with pkgs; { foo = "old"; bar = foo; } // overrides;
        overrides = { foo = "new"; };
      in pkgs.bar

  This evaluates to `"new"`, while previously it gave an “infinite recursion” error.

- Nix now has proper integer arithmetic operators. For instance, you can write `x + y` instead of `builtins.add x y`, or `x < y` instead of `builtins.lessThan x y`. The comparison operators also work on strings.

- On 64-bit systems, Nix integers are now 64 bits rather than 32 bits.

- When using the Nix daemon, the `nix-daemon` worker process now runs on the same CPU as the client, on systems that support setting CPU affinity. This gives a significant speedup on some systems.

- If a stack overflow occurs in the Nix evaluator, you now get a proper error message (rather than “Segmentation fault”) on some systems.

- In addition to directories, you can now bind-mount regular files in chroots through the (now misnamed) option `build-chroot-dirs`.

This release has contributions from Domen Kožar, Eelco Dolstra, Florian Friesdorf, Gergely Risko, Ivan Kozik, Ludovic Courtès and Shea Levy.