powershell behavior when host file handle is closed - windows

Question

I'm looking for an explanation (preferably documentation) of the following madness.
Say I have the following simple Perl script:
use strict;
use warnings;
my $output = "C:\\Temp\\aout.txt";
my $outpute = "C:\\Temp\\aoute.txt";
my $command = "powershell C:\\test.ps1";
close STDOUT;
close STDERR;
if ( (my $pid = fork()) == 0 ) {
open (STDOUT,">>$output") or die "cannot open $output as stdout: $!";
open (STDERR,">>$outpute") or die "cannot open $outpute as stderr: $!";
exec $command or die "couldn't exec $command: $!";
} else {
my $ret = waitpid($pid,0);
}
And that the Powershell script contains:
write-output "yay1";
write-error "nay2";
write-output "yay3";
write-error "nay4";
write-output "yay5";
write-error "nay6";
write-output "yay7";
write-error "nay8";
write-host "done!";
If I run the Perl script, it produces two files, as expected, with the following output:
aout.txt:
yay1
yay3
yay5
yay7
done!
aoute.txt:
C:\test.ps1 : nay2
At line:1 char:41
+ C:\test.ps1 <<<<
+ CategoryInfo : NotSpecified: (:) [Write-Error], WriteErrorException
+ FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException,test.ps1
C:\test.ps1 : nay4
At line:1 char:41
+ C:\test.ps1 <<<<
+ CategoryInfo : NotSpecified: (:) [Write-Error], WriteErrorException
+ FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException,test.ps1
C:\test.ps1 : nay6
At line:1 char:41
+ C:\test.ps1 <<<<
+ CategoryInfo : NotSpecified: (:) [Write-Error], WriteErrorException
+ FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException,test.ps1
C:\test.ps1 : nay8
At line:1 char:41
+ C:\test.ps1 <<<<
+ CategoryInfo : NotSpecified: (:) [Write-Error], WriteErrorException
+ FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException,test.ps1
If I modify the Perl script to keep STDERR closed before executing Powershell:
use strict;
use warnings;
my $output = "C:\\Temp\\aout.txt";
my $command = "powershell C:\\test.ps1";
close STDOUT;
close STDERR;
if ( (my $pid = fork()) == 0 ) {
open (STDOUT,">>$output") or die "cannot open $output as stdout: $!";
exec $command or die "couldn't exec $command: $!";
} else {
my $ret = waitpid($pid,0);
}
Then it produces one STDOUT file with all of the output:
yay1
C:\\test.ps1 : nay2
At line:1 char:41
+ C:\\test.ps1 <<<<
+ CategoryInfo : NotSpecified: (:) [Write-Error], WriteErrorException
+ FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException,test.ps1
yay3
C:\\test.ps1 : nay4
At line:1 char:41
+ C:\\test.ps1 <<<<
+ CategoryInfo : NotSpecified: (:) [Write-Error], WriteErrorException
+ FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException,test.ps1
yay5
C:\\test.ps1 : nay6
At line:1 char:41
+ C:\\test.ps1 <<<<
+ CategoryInfo : NotSpecified: (:) [Write-Error], WriteErrorException
+ FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException,test.ps1
yay7
C:\\test.ps1 : nay8
At line:1 char:41
+ C:\\test.ps1 <<<<
+ CategoryInfo : NotSpecified: (:) [Write-Error], WriteErrorException
+ FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException,test.ps1
done!
Is Powershell really realizing that STDERR is closed, and is doing a clean redirect onto STDOUT? Or is it the command line console? Or is it Perl?
For reference, this is on Windows Server 2003 x64 SP2 with:
C:\>perl --version
This is perl, v5.8.8 built for MSWin32-x64-multi-thread
(with 33 registered patches, see perl -V for more detail)
Copyright 1987-2006, Larry Wall
Binary build 819 [267479] provided by ActiveState http://www.ActiveState.com
Built Aug 27 2006 22:13:23
Perl may be copied only under the terms of either the Artistic License or the
GNU General Public License, which may be found in the Perl 5 source kit.
Complete documentation for Perl, including FAQ lists, should be found on
this system using "man perl" or "perldoc perl". If you have access to the
Internet, point your browser at http://www.perl.org/, the Perl Home Page.
C:\>powershell get-host
Name : ConsoleHost
Version : 2.0
InstanceId : 1ac67afa-f020-414c-b47b-031bdc8cc703
UI : System.Management.Automation.Internal.Host.InternalHostUserInterface
CurrentCulture : en-US
CurrentUICulture : en-US
PrivateData : Microsoft.PowerShell.ConsoleHost+ConsoleColorProxy
IsRunspacePushed : False
Runspace : System.Management.Automation.Runspaces.LocalRunspace
and this is part of an ongoing effort related to this and this.