使用 C# 捕获进程输出

Intro

很多时候我们可能会需要执行一段命令获取一个输出，遇到的比较典型的就是之前我们需要用 FFMpeg 实现视频的编码压缩水印等一系列操作，当时使用的是 FFMpegCore 这个类库，这个类库的实现原理是启动另外一个进程，启动 ffmpeg 并传递相应的处理参数，并根据进程输出获取处理进度

为了方便使用，实现了两个帮助类来方便的获取进程的输出，分别是 ProcessExecutor 和 CommandRunner，前者更为灵活，可以通过事件添加自己的额外事件订阅处理，后者为简化版，主要是只获取输出的场景，两者的实现原理大体是一样的，启动一个 Process，并监听其输出事件获取输出

ProcessExecutor

使用示例，这个示例是获取保存 nuget 包的路径的一个示例：

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 实现代码如下：

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

上面的这种方式比较灵活但有些繁琐，于是有了下面这个版本

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);
}

实现源码：

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

如果只要执行命令获取是否执行成功则使用 CommandRunner.Execute 即可，只获取输出和是否成功可以用 CommandRunner.ExecuteAndCapture 方法，如果想要进一步的添加事件订阅则使用 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

（编辑：李大同）

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