PowerShell 2.0: Quick Tip – Capture Verbose, Error & Warning Streams

update: missing backtick ` to escape the $verbosepreference variable

A question came up on stack overflow (you don’t know what that is? shame on you!) today from someone asking how they could capture the Verbose stream from a pipeline they ran in a C# program. As it turns out, the same technique is used in script, so I’ll give that example instead since I’m sure the C# guys and gals will have no problem converting the script.

The key is using the new (to v2.0) System.Management.Automation.PowerShell Type, which has a built-in Type Accelerator of [powershell]. It has a static method, Create, which is used to create an instance. This instance is pretty much ready to roll. It has a Streams property, which is of Type PSDataStreams. This Type has properties representing each collection of Error, Progress, Verbose, Debug and Warning.

$ps = [powershell]::create()
$ps.Commands.AddScript("`$verbosepreference='continue'; write-verbose 42")
$ps.invoke()
$ps.streams.verbose

Which yields the VerboseRecord that was written out:

Message InvocationInfo                              PipelineIterationInfo
------- --------------                              ---------------------
42      System.Management.Automation.InvocationInfo {0, 0}

What's important to note about the above example is that I had to set the $verbosepreference to at least "continue" (the default is silentlycontinue) in order for the verbose record to be written. Have fun!