在 .net 中捕获进程输出

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，处理结果等信息

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, string arguments = null, string workingDirectory = null){using var process = new Process(){StartInfo = new ProcessStartInfo(commandPath, arguments ?? string.Empty){UseShellExecute = false,CreateNoWindow = true,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