我如何检查进程是否有输出？

有没有办法表明像标准计算器这样的过程是否有输出，
我需要它，因为我有这一行：

sr = p1.StandardOutput;  

我需要这样做：

s = sr.ReadLine();  

仅当有输出时p1例如，在计算器中，没有输出，因此程序在ReadLine.
谢谢大家。

代码 ：

while (i < asProcesses.Length - 1)
            {
                if ((i + 1) == asProcesses.Length - 1 && sOutRedirect != "")
                    break;
                p1.StartInfo.RedirectStandardOutput = true;
                p1.StartInfo.FileName = asProcesses[i];
                p1.StartInfo.UseShellExecute = false;
                if(i==0)
                    p1.Start();
                sr = p1.StandardOutput;
                Process p2 = new Process();
                p2.StartInfo.RedirectStandardInput = true;
                p2.StartInfo.FileName = asProcesses[i + 1];
                p2.StartInfo.UseShellExecute = false;
                p2.Start();
                sw = p2.StandardInput;
                while (!sr.EndOfStream && s != null)
                {
                    s = sr.ReadLine();
                    if (s != null)
                    {
                        sw.WriteLine(s);
                    }
                }
                if (sw != null)
                    sw.Close();
                if (sr != null)
                    sr.Close();
                i++;
            }

void foo()
{
    System.Diagnostics.Process p = new System.Diagnostics.Process();
    p.StartInfo.FileName = "c:\\windows\\system32\\ping.exe";
    p.StartInfo.RedirectStandardOutput = true;
    p.StartInfo.UseShellExecute = false;
    p.EnableRaisingEvents = true;
    p.OutputDataReceived += new System.Diagnostics.DataReceivedEventHandler(p_OutputDataReceived);
    p.Start();
    p.BeginOutputReadLine();
}           

void p_OutputDataReceived(object sender, System.Diagnostics.DataReceivedEventArgs e)
{
    string s = e.Data;        
    // process s
}