---

description: Use build arguments to modify the app or its behaviour during build time

Build Arguments

{% hint style="info" %} This functionality requires at least auterion-app-api 3 to be available {% endhint %}

You may specify build-time arguments in the auterion-app.yml file using the build-args keyword:

{% code title="auterion-app.yml" %} yaml services: test-app: ssh: true build: . build-args: BAR: ${FOO} {% endcode %}

The environment variable FOO and the docker build argument BAR can then be defined in the environment where auterion-cli is executed, for example:

```bash

This will assign "123" to the BAR variable in the Dockerfile

FOO="123" auterion-cli app build ```

Alternatively the environment variable can be defined in a top-level .env file in the app directory:

{% code title=".env" %} ```yaml

This will also assign "123" to the BAR variable in the Dockerfile

FOO="123" ``` {% endcode %}

{% hint style="info" %} Note that environment variables defined from the command line will overwrite the variables already defined in the .env file. {% endhint %}

The BAR docker build argument can then be used at build-time from your Dockerfile:

{% code title="Dockerfile" %} ```docker FROM auterion/app-base:v2

ARG BAR RUN echo "My docker build arg is ${BAR}" ``` {% endcode %}