```gradle
def commandLineOf(command, terminal = null) {
    if (System.properties['os.name'].toLowerCase().contains('windows')) {
        return ['cmd', '/c', command]
    } else if (terminal != null) {
        return ['bash', '-c', terminal]
    } else {
        return ['bash', '-c', command]
    }
}

task example {
    doLast {
        exec {
            workingDir '.'
            commandLine commandLineOf("git fetch")
        }
        exec {
            workingDir '.'
            commandLine commandLineOf("dir", "ls")
        }
    }
}
```