使用 C# 捕獲進程輸出

使用 C# 捕獲進程輸出

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 實現視頻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進程，啟動 ffmpeg 並傳遞相應的處理參數，並根據進程輸出獲取處理進度

為了方便使用，實現了兩個幫助類來方便的獲取進程的輸出，分別是 ProcessExecutor 和 CommandRunner，前者更為靈活，可以通過事件添加自己的額外事件訂閱處理，后者為簡化版，主要是只獲取輸出的場景，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，這個示例是獲取保存 nuget 包的路徑的一個示例：

Copy

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 實現代碼如下：

Copy

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：

Copy

[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);
}

實現源碼：

Copy

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，如果想要進一步的添加事件訂閱則使用 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