Intro

很多時候我們可能會需要執行一段命令獲取一個輸出，遇到的比較典型的就是之前我們需要用 FFMpeg 實現視訊的編碼壓縮水印等一系列操作，當時使用的是 FFMpegCore 這個類庫，這個類庫的實現原理是啟動另外一個程序，啟動 ffmpeg 並傳遞相應的處理引數，並根據程序輸出獲取處理進度

為了方便使用，實現了兩個幫助類來方便的獲取程序的輸出，分別是 ProcessExecutor 和 CommandRunner，前者更為靈活，可以通過事件新增自己的額外事件訂閱處理，後者為簡化版，主要是隻獲取輸出的場景，兩者的實現原理大體是一樣的，啟動一個 Process，並監聽其輸出事件獲取輸出

ProcessExecutor

使用示例，這個示例是獲取儲存 nuget 包的路徑的一個示例：

using var executor = new ProcessExecutor("dotnet","nuget locals global-packages -l");
var folder = string.Empty;
executor.OnOutputDataReceived += (sender,str) =>
{
  if(str is null)
    return;

  Console.WriteLine(str);

  if(str.StartsWith("global-packages:"))
  {
    folder = str.Substring("global-packages:".Length).Trim();          
  }
};
executor.Execute();

Console.WriteLine(folder);

ProcessExecutor 實現程式碼如下：

public class ProcessExecutor : IDisposable
{
  public event EventHandler<int> OnExited;

  public event EventHandler<string> OnOutputDataReceived;

  public event EventHandler<string> OnErrorDataReceived;

  protected readonly Process _process;

  protected bool _started;

  public ProcessExecutor(string exePath) : this(new ProcessStartInfo(exePath))
  {
  }

  public ProcessExecutor(string exePath,string arguments) : this(new ProcessStartInfo(exePath,arguments))
  {
  }

  public ProcessExecutor(ProcessStartInfo startInfo)
  {
    _process = new Process()
    {
      StartInfo = startInfo,EnableRaisingEvents = true,};
    _process.StartInfo.UseShellExecute = false;
    _process.StartInfo.CreateNoWindow = true;
    _process.StartInfo.RedirectStandardOutput = true;
    _process.StartInfo.RedirectStandardInput = true;
    _process.StartInfo.RedirectStandardError = true;
  }

  protected virtual void InitializeEvents()
  {
    _process.OutputDataReceived += (sender,args) =>
    {
      if (args.Data != null)
      {
        OnOutputDataReceived?.Invoke(sender,args.Data);
      }
    };
    _process.ErrorDataReceived += (sender,args) =>
    {
      if (args.Data != null)
      {
        OnErrorDataReceived?.Invoke(sender,args.Data);
      }
    };
    _process.Exited += (sender,args) =>
    {
      if (sender is Process process)
      {
        OnExited?.Invoke(sender,process.ExitCode);
      }
      else
      {
        OnExited?.Invoke(sender,_process.ExitCode);
      }
    };
  }

  protected virtual void Start()
  {
    if (_started)
    {
      return;
    }
    _started = true;

    _process.Start();
    _process.BeginOutputReadLine();
    _process.BeginErrorReadLine();
    _process.WaitForExit();
  }

  public async virtual Task SendInput(string input)
  {
    try
    {
      await _process.StandardInput.WriteAsync(input!);
    }
    catch (Exception e)
    {
      OnErrorDataReceived?.Invoke(_process,e.ToString());
    }
  }

  public virtual int Execute()
  {
    InitializeEvents();
    Start();
    return _process.ExitCode;
  }

  public virtual async Task<int> ExecuteAsync()
  {
    InitializeEvents();
    return await Task.Run(() =>
    {
      Start();
      return _process.ExitCode;
    }).ConfigureAwait(false);
  }

  public virtual void Dispose()
  {
    _process.Dispose();
    OnExited = null;
    OnOutputDataReceived = null;
    OnErrorDataReceived = null;
  }
}

CommandExecutor

上面的這種方式比較靈活但有些繁瑣，於是有了下面這個版本

使用示例：

[Fact]
public void HostNameTest()
{
  if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
  {
    return;
  }

  var result = CommandRunner.ExecuteAndCapture("hostname");

  var hostName = Dns.GetHostName();
  Assert.Equal(hostName,result.StandardOut.TrimEnd());
  Assert.Equal(0,result.ExitCode);
}

實現原始碼：

public static class CommandRunner
{
  public static int Execute(string commandPath,string arguments = null,string workingDirectory = null)
  {
    using var process = new Process()
    {
      StartInfo = new ProcessStartInfo(commandPath,arguments ?? string.Empty)
      {
        UseShellExecute = false,CreateNoWindow = true,WorkingDirectory = workingDirectory ?? Environment.CurrentDirectory
      }
    };

    process.Start();
    process.WaitForExit();
    return process.ExitCode;
  }

  public static CommandResult ExecuteAndCapture(string commandPath,RedirectStandardOutput = true,RedirectStandardError = true,WorkingDirectory = workingDirectory ?? Environment.CurrentDirectory
      }
    };
    process.Start();
    var standardOut = process.StandardOutput.ReadToEnd();
    var standardError = process.StandardError.ReadToEnd();
    process.WaitForExit();
    return new CommandResult(process.ExitCode,standardOut,standardError);
  }
}

public sealed class CommandResult
{
  public CommandResult(int exitCode,string standardOut,string standardError)
  {
    ExitCode = exitCode;
    StandardOut = standardOut;
    StandardError = standardError;
  }

  public string StandardOut { get; }
  public string StandardError { get; }
  public int ExitCode { get; }
}

More

如果只要執行命令獲取是否執行成功則使用 CommandRunner.Execute 即可，只獲取輸出和是否成功可以用 CommandRunner.ExecuteAndCapture 方法，如果想要進一步的新增事件訂閱則使用 ProcessExecutor

Reference

https://github.com/rosenbjerg/FFMpegCore
https://github.com/WeihanLi/WeihanLi.Common/blob/dev/src/WeihanLi.Common/Helpers/ProcessExecutor.cs
https://github.com/WeihanLi/WeihanLi.Common/blob/dev/test/WeihanLi.Common.Test/HelpersTest/ProcessExecutorTest.cs
https://github.com/WeihanLi/WeihanLi.Common/blob/dev/test/WeihanLi.Common.Test/HelpersTest/CommandRunnerTest.cs

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