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, 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
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