It is good practice in Gradle to use lazy configuration. This makes builds faster as only configuration values are evaluated when needed. We should try to not let Gradle spend time on evaluating configuration values that will not be used. For example tasks that are not executed could still be configured by Gradle. If we make sure the configuration of these tasks is lazy we can save time.

Gradle gives us a lazy way to get the value of an environment variable. In our build script we can use the providers property of type ProviderFactory and the method environmentVariable(String). This method returns a Provider<String> instance that can be used to get the value of an environment variable in a lazy way.

In the following example we register a task that prints the value of the environment variable USER. We use lazy configuration to make sure the value of the environment variable is only fetched when the task is executed.

tasks {
    register<PrintEnvironmentVariable>("printEnvironmentVariable") {
        // We can use providers.environmentVariable(String)
        // to get the value of an environment variable
        // in a lazy way.
        // The argument can also be a Provider<String> type.
        // So at this point the value is not fetched yet,
        // only when the task is executed the actual value
        // of the environment variable "USER" is fetched.
        environmentVariable = providers.environmentVariable("USER")
    }
}

// Simple task to print the value of an environment variable.
abstract class PrintEnvironmentVariable : DefaultTask() {
    @get:Input
    abstract val environmentVariable: Property<String> // Use lazy property.

    @TaskAction
    fun printEnvironmentVariable() {
        // Only here we actually will get the value
        // for the environment variable.
        logger.quiet(environmentVariable.get())
    }
}

When we execute the tasks we see the value of the environment variable USER:

$ ./gradlew printEnvironmentVariable printEnvironmentVariable2

> Task :printEnvironmentVariable
mrhaki

> Task :printEnvironmentVariable2
mrhaki

BUILD SUCCESSFUL in 599ms
2 actionable tasks: 2 executed

Written with Gradle 8.6.

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