如何在Linux上使用Java或JRuby找到我的PID？

import java.lang.ProcessHandle;

public class Main {
    public static void main(String[] args) {
        ProcessHandle processHandle = ProcessHandle.current();
        long pid = processHandle.pid();
        System.out.println("My PID is: " + pid);
    }
}

require 'etc'

pid = Process.pid
puts "My PID is: #{pid}"