Gradle: Get standard output text

build.gradle

ant.condition(property: "os", value: "windows") { os(family: "windows") }
ant.condition(property: "os", value: "unix" ) { os(family: "unix") }

task execCommandLine(type:Exec) {
    switch(ant.properties.os){
        case 'windows':
            commandLine 'cmd', '/c', 'echo', 'hello'
            break
        case 'unix':
            commandLine 'echo', 'hello'
            break
    }
    standardOutput = new ByteArrayOutputStream()
}

execCommandLine.doFirst {
    println 'doFirst'
    print standardOutput.toString()
}

execCommandLine << {
    println 'doLast'
    print standardOutput.toString()
}