Powershell 不捕获 perl 的标准输出

Question

I have the following simple script in powershell (say under C:\\Users\\myusername\\Desktop\\tests\\test.ps1 )

$counter = 0
while (1) {
    $counter++
    if ($counter % 2) {
        [Console]::Error.WriteLine("($counter) This is an error")
    } else {
        echo "($counter) Some output"
    }
    sleep 1
}

I want to programmatically invoke this script and capture its standard output and standard error into a file (say C:\\Users\\myusername\\Desktop\\test.log ). For that I wrote the following powershell script:

$psi = New-object System.Diagnostics.ProcessStartInfo
$psi.CreateNoWindow = $true
$psi.UseShellExecute = $false
$psi.RedirectStandardOutput = $true
$psi.RedirectStandardError = $true
$psi.FileName = 'C:\Windows\system32\WindowsPowerShell\v1.0\powershell.exe'
$psi.Arguments = @('C:\Users\myusername\Desktop\tests\test.ps1')

$process = New-Object System.Diagnostics.Process
$process.StartInfo = $psi

$logAction = {
    $time = Get-Date -Format o
    Add-Content 'C:\Users\myusername\Desktop\test.log' "($time)[$($Event.MessageData)]: $($Event.SourceArgs.Data)"
}

Register-ObjectEvent -InputObject $process -EventName ErrorDataReceived -Action $logAction -MessageData "STDERR" >$null
Register-ObjectEvent -InputObject $process -EventName OutputDataReceived -Action $logAction -MessageData "STDOUT" >$null

$process.Start() >$null
$process.BeginErrorReadLine() >$null
$process.BeginOutputReadLine() >$null

$process.Id

The content of the test.log file is as expected:

(2018-12-05T15:00:45.7615056+01:00)[STDERR]: (1) This is an error
(2018-12-05T15:00:47.0119743+01:00)[STDOUT]: (2) Some output
(2018-12-05T15:00:47.9497710+01:00)[STDERR]: (3) This is an error
(2018-12-05T15:00:49.8253980+01:00)[STDOUT]: (4) Some output
(2018-12-05T15:00:49.8253980+01:00)[STDERR]: (5) This is an error
(2018-12-05T15:00:51.2008546+01:00)[STDOUT]: (6) Some output
(2018-12-05T15:00:51.8260768+01:00)[STDERR]: (7) This is an error
(2018-12-05T15:01:03.6269252+01:00)[STDERR]:
(2018-12-05T15:01:03.6269252+01:00)[STDOUT]:

But now comes the interesting part. I have the following perl script (say under C:\\Users\\myusername\\Desktop\\tests\\test.pl ) which I run in Windows using Strawberry Perl , and which pretty much resembles the first powershell script in my question:

#!/usr/bin/perl

use strict;
use warnings;

my $counter = 0;

while (1) {
    $counter++;

    if ($counter % 2) {
        print STDERR "($counter) This is an error!\n";
    } else {
        print STDOUT "($counter) Some message\n";
    }

    sleep 1;
}

I also want to programmatically invoke this script and capture its standard output and standard error into a file. For that I change the second script in my question by updating the $psi.FileName and $psi.Arguments values to:

$psi.FileName = 'C:\Strawberry\perl\bin\perl.exe'
$psi.Arguments = @('C:\Users\myusername\Desktop\tests\test.pl')

But now the content of the test.log file is not what I expected

(2018-12-05T14:14:53.9176561+01:00)[STDERR]: (1) This is an error!
(2018-12-05T14:14:55.7926306+01:00)[STDERR]: (3) This is an error!
(2018-12-05T14:14:57.9801317+01:00)[STDERR]: (5) This is an error!
(2018-12-05T14:15:22.2301618+01:00)[STDOUT]:
(2018-12-05T14:15:22.2301618+01:00)[STDERR]:

As you can see the standard output is not getting captured. I have absolutely no idea why is this happening and how can I solve it. Why is it not working for perl but it does for powershell? How can I get it to work with perl?

My powershell version is 5.1.17134.407 on a Windows 10 Pro.

Answer 1

STDERR is usually set up for auto-flush, STDOUT is not. Your code expects to receive every output line as it is written.

Try adding the following 2 lines to your Perl script after use warnings;

use IO::Handle;
STDOUT->autoflush(1);