collection of preference variables in Powershell - powershell

Question

I'm looking into importing my entire set of preference variables into a remote scope. Does PowerShell implement collections of variables? Is there a collection of preference variables? If so, would I be able to import the collection with $using: ?
Something like:
Begin {
$scriptblock = {
Try {
$VerbosePreference = $Using:VerbosePreference
$ErrorActionPreference = $Using:ErrorActionPreference
...
}
Catch{ #Ignore these errors }
...
I'd like to import all the preference variables without specifying individually if possible...

Answer 1

PowerShell (as of v5.1):
doesn't implement collections of variables,
and there is no programmatic way to unambiguously and exhaustively identify all preference variables.
For the current list of all preference variables, see Get-Help about_Preference_Variables.
That said, you can use wildcard expression *Preference with Get-Variable to locate at least some of the preference variables - and perhaps they cover your needs:
> (Get-Variable *Preference).Name
ConfirmPreference
DebugPreference
ErrorActionPreference
InformationPreference
ProgressPreference
VerbosePreference
WarningPreference
WhatIfPreference
As stated, the results are neither guaranteed to be complete (e.g., MaximumHistoryCount is not matched), nor do they exclude potential false positives (nothing prevents you from defining variable $FooPreference, for instance).
If you're willing to extract all variable names from about_Preference_Variables help topic - which is not fully robust - see the bottom of this post.
Overall, the best approximation is probably the following command:
> Get-Variable |
Where-Object {
$_.Name -clike '*Preference' -or
($_.Attributes -and $_.Options -notcontains 'ReadOnly')
} | % Name
ConfirmPreference
DebugPreference
ErrorActionPreference
InformationPreference
MaximumAliasCount
MaximumDriveCount
MaximumErrorCount
MaximumFunctionCount
MaximumHistoryCount
MaximumVariableCount
OutputEncoding
ProgressPreference
PSDefaultParameterValues
VerbosePreference
WarningPreference
WhatIfPreference
This relies on the assumption that only preference variables have (validation) attributes, which is typically true, but, again, you're free to define your own variables with validation attributes, which would then mistakenly be included too.
$_.Options -notcontains 'ReadOnly' weeds out read-only variables, because, by definition, they can't be preference variables if they cannot be modified.
As for using these variables in a remote command / a background job:
There is no elegant solution (and $using: only works with literal variable names), but you can try the following:
# Collect pref. variables, to the best of our ability.
$prefVarDefs = Get-Variable | ? { $_.Name -clike '*Preference' -or ($_.Attributes -and $_.Options -notcontains 'ReadOnly') }
# Pass them to the background/remote script block and have them
# assigned there.
Start-Job { $args | % { set-variable $_.Name $_.Value }; ... } -Args $prefVarDefs
Note that Start-Job is used as an example (because it can be run without remoting and in a non-elevated session), but the same rules apply as with Invoke-Command, for instance, and the same technique can be used with the latter.
Another option is to parse the about_Preference_Variables help topic, which is somewhat brittle however, because it:
relies on the topic's specific formatting
relies on the topic to be both complete and accurate.
(Get-Help about_Preference_Variables) -creplace '(?s)\A.*?\r?\n +?Variable +Default Value\r?\n +?-+ +-+\r?\n(.+?)\r?\n\r?\n.*\Z', '$1' -split '\r?\n' | % { (-split $_)[0] }