如何在powershell中异步捕获进程输出? [英] How to capture process output asynchronously in powershell?

问题描述

我想从我在 Powershell 脚本中启动的进程中捕获 stdout 和 stderr 并将其异步显示到控制台.我通过 MSDN 和 其他博客.

I want to capture stdout and stderr from a process that I start in a Powershell script and display it asynchronously to the console. I've found some documentation on doing this through MSDN and other blogs.

创建并运行下面的示例后，我似乎无法异步显示任何输出.所有输出仅在进程终止时显示.

After creating and running the example below, I can't seem to get any output to be displayed asynchronously. All of the output is only displayed when the process terminates.

$ps = new-object System.Diagnostics.Process
$ps.StartInfo.Filename = "cmd.exe"
$ps.StartInfo.UseShellExecute = $false
$ps.StartInfo.RedirectStandardOutput = $true
$ps.StartInfo.Arguments = "/c echo `"hi`" `& timeout 5"

$action = { Write-Host $EventArgs.Data  }
Register-ObjectEvent -InputObject $ps -EventName OutputDataReceived -Action $action | Out-Null

$ps.start() | Out-Null
$ps.BeginOutputReadLine()
$ps.WaitForExit()

在这个例子中，我希望在程序执行结束之前在命令行上看到hi"的输出，因为应该触发了 OutputDataReceived 事件.

In this example, I was expecting to see the output of "hi" on the commandline before the end of program execution because the OutputDataReceived event should have been triggered.

我已经尝试过使用其他可执行文件 - java.exe、git.exe 等.所有这些都具有相同的效果，所以我认为有一些简单的东西我不理解或没有错过了.异步读取标准输出还需要做什么?

I've tried this using other executables - java.exe, git.exe, etc. All of them have the same effect, so I'm left to think that there is something simple that I'm not understanding or have missed. What else needs to be done to read stdout asynchronously?

推荐答案

不幸的是，如果您想正确地进行异步阅读，那么它并不是那么容易.如果你在没有超时的情况下调用 WaitForExit() 你可以使用我写的这个函数(基于 C# 代码):

Unfortunately asynchronous reading is not that easy if you want to do it properly. If you call WaitForExit() without timeout you could use something like this function I wrote (based on C# code):

function Invoke-Executable {
    # Runs the specified executable and captures its exit code, stdout
    # and stderr.
    # Returns: custom object.
    param(
        [Parameter(Mandatory=$true)]
        [ValidateNotNullOrEmpty()]
        [String]$sExeFile,
        [Parameter(Mandatory=$false)]
        [String[]]$cArgs,
        [Parameter(Mandatory=$false)]
        [String]$sVerb
    )

    # Setting process invocation parameters.
    $oPsi = New-Object -TypeName System.Diagnostics.ProcessStartInfo
    $oPsi.CreateNoWindow = $true
    $oPsi.UseShellExecute = $false
    $oPsi.RedirectStandardOutput = $true
    $oPsi.RedirectStandardError = $true
    $oPsi.FileName = $sExeFile
    if (! [String]::IsNullOrEmpty($cArgs)) {
        $oPsi.Arguments = $cArgs
    }
    if (! [String]::IsNullOrEmpty($sVerb)) {
        $oPsi.Verb = $sVerb
    }

    # Creating process object.
    $oProcess = New-Object -TypeName System.Diagnostics.Process
    $oProcess.StartInfo = $oPsi

    # Creating string builders to store stdout and stderr.
    $oStdOutBuilder = New-Object -TypeName System.Text.StringBuilder
    $oStdErrBuilder = New-Object -TypeName System.Text.StringBuilder

    # Adding event handers for stdout and stderr.
    $sScripBlock = {
        if (! [String]::IsNullOrEmpty($EventArgs.Data)) {
            $Event.MessageData.AppendLine($EventArgs.Data)
        }
    }
    $oStdOutEvent = Register-ObjectEvent -InputObject $oProcess `
        -Action $sScripBlock -EventName 'OutputDataReceived' `
        -MessageData $oStdOutBuilder
    $oStdErrEvent = Register-ObjectEvent -InputObject $oProcess `
        -Action $sScripBlock -EventName 'ErrorDataReceived' `
        -MessageData $oStdErrBuilder

    # Starting process.
    [Void]$oProcess.Start()
    $oProcess.BeginOutputReadLine()
    $oProcess.BeginErrorReadLine()
    [Void]$oProcess.WaitForExit()

    # Unregistering events to retrieve process output.
    Unregister-Event -SourceIdentifier $oStdOutEvent.Name
    Unregister-Event -SourceIdentifier $oStdErrEvent.Name

    $oResult = New-Object -TypeName PSObject -Property ([Ordered]@{
        "ExeFile"  = $sExeFile;
        "Args"     = $cArgs -join " ";
        "ExitCode" = $oProcess.ExitCode;
        "StdOut"   = $oStdOutBuilder.ToString().Trim();
        "StdErr"   = $oStdErrBuilder.ToString().Trim()
    })

    return $oResult
}

它捕获标准输出、标准错误和退出代码.示例用法:

It captures stdout, stderr and exit code. Example usage:

$oResult = Invoke-Executable -sExeFile 'ping.exe' -cArgs @('8.8.8.8', '-a')
$oResult | Format-List -Force 

有关更多信息和替代实现(在 C# 中)阅读这篇博文.

For more info and alternative implementations (in C#) read this blog post.

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