Use of Preference Variables to control behavior of streams
PSMDTAG:FAQ: Why don't I see output when I use Write-Verbose and Write-Debug?
PSMDTAG:SHELL: Use of Preference Variables to control behavior of streams.
In Windows PowerShell, the WRITE-XXX cmdlets merely sends things to a Named stream. You then have user-defined preferences for what to do when things appear on that stream. Alex Angelopoulos provided the following function TEST-WRITER to highlight the issue:
function Test-Writer
{
'Will test Write -Host, -Output, -Verbose, -Warning, -Error.'
Write-Host 'Write-Host'
Write-Output 'Write-Output'
Write-Verbose 'Write-Verbose'
Write-Warning 'Write-Warning'
Write-Error 'Write-Error'
'Done with test.'
}
PS> test-writer
Will test Write -Host, -Output, -Verbose, -Warning, -Error.
Write-Host
Write-Output
WARNING: Write-Warning
Test-Writer : Write-Error
At line:1 char:11
+ test-writer <<<<
Done with test.
Notice the lack of "Write-Verbose" and "Write-Debug"
PS> dir variable:*preference
Name Value
---- -----
DebugPreference SilentlyContinue
VerbosePreference SilentlyContinue
ProgressPreference Continue
ErrorActionPreference Continue
WhatIfPreference 0
WarningPreference Continue
ConfirmPreference High
PS> $DebugPreference=$VerbosePreference="Continue"
PS> test-writer
Will test Write -Host, -Output, -Verbose, -Warning, -Error.
Write-Host
Write-Output
VERBOSE: Write-Verbose
WARNING: Write-Warning
Test-Writer : Write-Error
At line:1 char:11
+ test-writer <<<<
Done with test.
PS>
Enjoy!
Jeffrey Snover [MSFT]
Windows PowerShell Architect
Visit the Windows PowerShell Team blog at: http://blogs.msdn.com/PowerShell
Visit the Windows PowerShell ScriptCenter at: http://www.microsoft.com/technet/scriptcenter/hubs/msh.mspx
