# `mix compile.appup`
[🔗](https://github.com/ausimian/forecastle/blob/1.0.0/lib/mix/tasks/compile/appup.ex#L1)

Compiles appup source into the application's `ebin` directory.

Configure the source with the `:appup` project key, relative to `mix.exs`:

    def project do
      [
        appup: "appup.exs",
        compilers: Mix.compilers() ++ [:appup]
      ]
    end

The source is evaluated for its value and must not introduce top-level
bindings. The compiler writes `<app>.appup` beside the application's BEAM
files on every build.

A configured but missing source is a compilation error. When the source or
project key is removed, the compiler deletes stale output. To disable appups
for one environment, keep the compiler registered and set `:appup` to `nil`.

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*Consult [api-reference.md](api-reference.md) for complete listing*