# Trivial builders

Nixpkgs provides a couple of functions that help with building derivations. The most important one, `stdenv.mkDerivation`, has already been documented above. The following functions wrap `stdenv.mkDerivation`, making it easier to use in certain cases.

`runCommand`

  This takes three arguments, `name`, `env`, and `buildCommand`. `name` is just the name that Nix will append to the store path in the same way that `stdenv.mkDerivation` uses its `name` attribute. `env` is an attribute set specifying environment variables that will be set for this derivation. These attributes are then passed to the wrapped `stdenv.mkDerivation`. `buildCommand` specifies the commands that will be run to create this derivation. Note that you will need to create `$out` for Nix to register the command as successful.

  An example of using `runCommand` is provided below.

             (import <nixpkgs> {}).runCommand "my-example" {} ''
               echo My example command is running

               mkdir $out

               echo I can write data to the Nix store > $out/message

               echo I can also run basic commands like:

               echo ls
               ls

               echo whoami
               whoami

               echo date
               date
             ''

`runCommandCC`

  This works just like `runCommand`. The only difference is that it also provides a C compiler in `buildCommand`’s environment. To minimize your dependencies, you should only use this if you are sure you will need a C compiler as part of running your command.

`writeTextFile`, `writeText`, `writeTextDir`, `writeScript`, `writeScriptBin`

  These functions write `text` to the Nix store. This is useful for creating scripts from Nix expressions. `writeTextFile` takes an attribute set and expects two arguments, `name` and `text`. `name` corresponds to the name used in the Nix store path. `text` will be the contents of the file. You can also set `executable` to true to make this file have the executable bit set.

  Many more commands wrap `writeTextFile` including `writeText`, `writeTextDir`, `writeScript`, and `writeScriptBin`. These are convenience functions over `writeTextFile`.

`symlinkJoin`

  This can be used to put many derivations into the same directory structure. It works by creating a new derivation and adding symlinks to each of the paths listed. It expects two arguments, `name`, and `paths`. `name` is the name used in the Nix store path for the created derivation. `paths` is a list of paths that will be symlinked. These paths can be to Nix store derivations or any other subdirectory contained within.