Realise a derivation

Building a derivation is referred to as "realisation". A derivation is just an abstract description of a package, based upon what it requires to build. Derivations can be thought of as constructing a blueprint, but realisation is the construction of the desired object. Taking from the previous example, one can build a derivations like so:

$ nix-store --realise /nix/store/byqskk0549v1zz1b2a61lb7llfn4h5bw-hello-2.10.drv

# or in nix flakes:

$ nix build nixpkgs#hello

Here, the gnu hello project was built and installed at the output path. This includes: the executable binary, documenation, and locale info.

$ tree -L 2 /nix/store/f4bywv8hjwl0ckv7l077pnap81h6qxw4-hello-2.10
├── bin
│   └── hello
└── share
    ├── info
    ├── locale
    └── man

The nix-build and nix build commands will perform both instantiation and realisation. These are the most common commands used when iterating on packages. One could also do:

$ nix-buid '<nixpkgs>' -A hello
# these are the same, nix build is just much more concise
$ nix-store --realise $(nix-instantiate '<nixpkgs>' -A hello)

Note: Many other commands also will realise a derivation as part of a workflow. Some examples are: nix-shell, nix shell, nix-env, nix run, and nix profile. These commands are very goal oriented and will differ significantly in how they leverage nix, often realisation is an side-effect to achieve that goal.