# Release 0.10 (2006-10-06)

> **Note**
> 
> This version of Nix uses Berkeley DB 4.4 instead of 4.3. The database
> is upgraded automatically, but you should be careful not to use old
> versions of Nix that still use Berkeley DB 4.3. In particular, if you
> use a Nix installed through Nix, you should run
> 
>     $ nix-store --clear-substitutes
> 
> first.

> **Warning**
> 
> Also, the database schema has changed slighted to fix a performance
> issue (see below). When you run any Nix 0.10 command for the first
> time, the database will be upgraded automatically. This is
> irreversible.

  - `nix-env` usability improvements:
    
      - An option `--compare-versions` (or `-c`) has been added to
        `nix-env
                                                        --query` to allow you to compare installed versions of packages
        to available versions, or vice versa. An easy way to see if you
        are up to date with what’s in your subscribed channels is
        `nix-env -qc \*`.
    
      - `nix-env --query` now takes as arguments a list of package names
        about which to show information, just like `--install`, etc.:
        for example, `nix-env -q gcc`. Note that to show all
        derivations, you need to specify `\*`.
    
      - `nix-env -i
                                                        pkgname` will now install the highest available version of
        *pkgname*, rather than installing all available versions (which
        would probably give collisions) (`NIX-31`).
    
      - `nix-env (-i|-u) --dry-run` now shows exactly which missing
        paths will be built or substituted.
    
      - `nix-env -qa --description` shows human-readable descriptions of
        packages, provided that they have a `meta.description` attribute
        (which most packages in Nixpkgs don’t have yet).

  - New language features:
    
      - Reference scanning (which happens after each build) is much
        faster and takes a constant amount of memory.
    
      - String interpolation. Expressions like
        
            "--with-freetype2-library=" + freetype + "/lib"
        
        can now be written as
        
            "--with-freetype2-library=${freetype}/lib"
        
        You can write arbitrary expressions within `${...}`, not just
        identifiers.
    
      - Multi-line string literals.
    
      - String concatenations can now involve derivations, as in the
        example `"--with-freetype2-library="
                                                        + freetype + "/lib"`. This was not previously possible because
        we need to register that a derivation that uses such a string is
        dependent on `freetype`. The evaluator now properly propagates
        this information. Consequently, the subpath operator (`~`) has
        been deprecated.
    
      - Default values of function arguments can now refer to other
        function arguments; that is, all arguments are in scope in the
        default values (`NIX-45`).
    
      - Lots of new built-in primitives, such as functions for list
        manipulation and integer arithmetic. See the manual for a
        complete list. All primops are now available in the set
        `builtins`, allowing one to test for the availability of primop
        in a backwards-compatible way.
    
      - Real let-expressions: `let x = ...;
                                                        ... z = ...; in ...`.

  - New commands `nix-pack-closure` and `nix-unpack-closure` than can be
    used to easily transfer a store path with all its dependencies to
    another machine. Very convenient whenever you have some package on
    your machine and you want to copy it somewhere else.

  - XML support:
    
      - `nix-env -q --xml` prints the installed or available packages in
        an XML representation for easy processing by other tools.
    
      - `nix-instantiate --eval-only
                                                        --xml` prints an XML representation of the resulting term. (The