# Release 1.9 (2015-06-12)

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

  - Signed binary cache support. You can enable signature checking by
    adding the following to `nix.conf`:
    
        signed-binary-caches = *
        binary-cache-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
    
    This will prevent Nix from downloading any binary from the cache
    that is not signed by one of the keys listed in
    `binary-cache-public-keys`.
    
    Signature checking is only supported if you built Nix with the
    `libsodium` package.
    
    Note that while Nix has had experimental support for signed binary
    caches since version 1.7, this release changes the signature format
    in a backwards-incompatible way.

  - Automatic downloading of Nix expression tarballs. In various places,
    you can now specify the URL of a tarball containing Nix expressions
    (such as Nixpkgs), which will be downloaded and unpacked
    automatically. For example:
    
      - In `nix-env`:
        
            $ nix-env -f https://github.com/NixOS/nixpkgs-channels/archive/nixos-14.12.tar.gz -iA firefox
        
        This installs Firefox from the latest tested and built revision
        of the NixOS 14.12 channel.
    
      - In `nix-build` and `nix-shell`:
        
            $ nix-build https://github.com/NixOS/nixpkgs/archive/master.tar.gz -A hello
        
        This builds GNU Hello from the latest revision of the Nixpkgs
        master branch.
    
      - In the Nix search path (as specified via `NIX_PATH` or `-I`).
        For example, to start a shell containing the Pan package from a
        specific version of Nixpkgs:
        
            $ nix-shell -p pan -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/8a3eea054838b55aca962c3fbde9c83c102b8bf2.tar.gz
    
      - In `nixos-rebuild` (on NixOS):
        
            $ nixos-rebuild test -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-unstable.tar.gz
    
      - In Nix expressions, via the new builtin function `fetchTarball`:
        
            with import (fetchTarball https://github.com/NixOS/nixpkgs-channels/archive/nixos-14.12.tar.gz) {}; …
        
        (This is not allowed in restricted mode.)

  - `nix-shell` improvements:
    
      - `nix-shell` now has a flag `--run` to execute a command in the
        `nix-shell` environment, e.g. `nix-shell --run make`. This is
        like the existing `--command` flag, except that it uses a
        non-interactive shell (ensuring that hitting Ctrl-C won’t drop
        you into the child shell).
    
      - `nix-shell` can now be used as a `#!`-interpreter. This allows
        you to write scripts that dynamically fetch their own
        dependencies. For example, here is a Haskell script that, when
        invoked, first downloads GHC and the Haskell packages on which
        it depends:
        
            #! /usr/bin/env nix-shell
            #! nix-shell -i runghc -p haskellPackages.ghc haskellPackages.HTTP
            
            import Network.HTTP
            
            main = do
              resp <- Network.HTTP.simpleHTTP (getRequest "http://nixos.org/")