How to detect the current OS from Gradle

Mid 2020 Update: Still incubating:

OperatingSystem os = org.gradle.nativeplatform.platform.internal.DefaultNativePlatform.currentOperatingSystem; 

Early 2019 Update: current() removed.

org.gradle.nativeplatform.platform.OperatingSystem.getDisplayName()

org.gradle.nativeplatform.platform.OperatingSystem.isLinux()

Keep in mind that it's still incubating though.

Mid 2018 Update: just like it was mentioned in comments, now this class moved to a different package, so one should use org.gradle.nativeplatform.platform.OperatingSystem.current()

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As of mid 2015, Peter Kahn's answer is still valid. Environment-based profile activation is still something done relatively easier in Maven. But keep in mind that org.apache.tools.ant.taskdefs.condition.Os.isFamily is not exclusive in the sense that if it returns true with one particular parameter it is not necessarily means that it returns false for any other parameter. For instance:

import org.apache.tools.ant.taskdefs.condition.Os
task detect {
    doLast {
        println(Os.isFamily(Os.FAMILY_WINDOWS))
        println(Os.isFamily(Os.FAMILY_MAC))
        println(Os.isFamily(Os.FAMILY_UNIX))
    }
}

It will return true both for Os.FAMILY_MAC and Os.FAMILY_UNIX on MacOS. Usually it is not something you need in build scripts.

There is though another way to achieve this using Gradle 2+ API, namely:

import org.gradle.internal.os.OperatingSystem;

task detect {
    doLast {
        println(OperatingSystem.current().isMacOsX())
        println(OperatingSystem.current().isLinux())
    }
}

Check out the documentation for the org.gradle.nativeplatform.platform.OperatingSystem interface. It is worth to mention that this interface is marked with incubating annotation, that is, "the feature is currently a work-in-progress and may change at any time". The "internal" namespace in the implementation also gives us a hint that we should use this knowing that this can change.

But personally I'd go with this solution. It's just that it's better to write a wrapper class so as not to mess up in case something will change in the future.

Actually, I looked at the Gradle project, and this looks a little cleaner as it uses Ant's existing structure:

import org.apache.tools.ant.taskdefs.condition.Os

task checkWin() << {
    if (Os.isFamily(Os.FAMILY_WINDOWS)) {
        println "*** Windows "
    }
}

I found this in the following Gradle branch, and it seems to work nicely. gradle/gradle-core/branches/RB-0.3/build.gradle