Passing Configuration to a Gradle Build via Custom Environment Variables

Internal

• Gradle Variables and Properties
• Gradle Operations

Overview

This article describes a generic method to pass configuration to a Gradle build using custom environment variables. This method could prove useful when Gradle builds are executed in containers, as it is the case for AWS CodeBuild builds.

Playground

https://github.com/ovidiuf/playground/tree/master/gradle/custom-environment-variables

Procedure

The method consists in defining a project extra property that is initialized with the value of the custom environment variable, or to a default value if the environment variable is not defined. The following code sequence is added to build.gradle, in the ext closure:

ext {

    projectExtPropertyInformedByEnvironmentVariable = "default value"

    String s = System.getenv("CUSTOM_ENVIRONMENT_VARIABLE");
    if (s != null) {

        projectExtPropertyInformedByEnvironmentVariable = s;
    }
}

The following task displays the property value:

ask display {

    println projectExtPropertyInformedByEnvironmentVariable
}

If CUSTOM_ENVIRONMENT_VARIABLE is not set, executing the "display" task results in:

gradle display
> Configure project :
default value
BUILD SUCCESSFUL in 0s

Setting the environment variable propagates it to the build:

export CUSTOM_ENVIRONMENT_VARIABLE=BLAH
gradle display
> Configure project :
BLAH
BUILD SUCCESSFUL in 0s

If you need to stop the build with an error if the environment variable is not found in the environment, see:

Stop a Gradle Build with an Error