Tag Archives: Get-Help

Three Ways to Set $PSDefaultParameterValues

Update: When you’re done here, read Part II.

Although we’ve discussed the $PSDefaultParameterValues before, I wanted to a do a quick recap. I need one place that shows the various ways to set this variable. That’s what this post will do for me, and perhaps you too.

First, however, let’s remind everyone what the $PSDefaultParameterValues variable does for us. It allows us to set a custom, default value for a function, or cmdlet’s parameter. One of the examples I mentioned before, in one of the three posts I’ve written about $PSDefaultParameterValues (1 | 2 | 3), used Get-Help.

This cmdlet includes a ShowWindow switch parameter that will open the full help inside its own GUI window. I tend to use this option a great deal to keep my ConsoleHost clean. In order to keep this post short, I’m just going to write the three ways in which I’m aware that we can set this variable.

$PSDefaultParameterValues.Add('Get-Help:ShowWindow',$true)

$PSDefaultParameterValues = @{'Get-Help:ShowWindow' = $true}

$PSDefaultParameterValues['Get-Help:ShowWindow'] = $true

Oh, Lee Holmes posted a welcome PSDefaultParameterValues addition on Twitter recently. I’ve included that addition below using the three above options, as well. Unlike his example, I moved from three underscores, to two. You’ll see what I mean below, if you haven’t already read the Tweet.

With this example in place, the results of all the commands entered will end up in the $__ variable. Again, that’s two underscores. Run a Get-ADUser command, for instance, and you’ll get the results both on the screen, and in the $__ variable up until you run another command that can make use of the OutVariable common parameter.

$PSDefaultParameterValues.Add('Out-Default:OutVariable','__')

$PSDefaultParameterValues = @{'Out-Default:OutVariable' = '__'}

$PSDefaultParameterValues['Out-Default:OutVariable'] = '__'

Give a Parameter a Default Value (Part III)

Part II: http://tommymaynard.com/quick-learn-give-a-parameter-a-default-value-part-ii-2015

Didn’t know I’d be back for a third installment of this topic, but the $PSDefaultParameterValues variable is still such a huge convenience. While punching out commands today, I had a thought: Can $PSDefaultParameterValues be a bit more dynamic?

I’m not going to fully introduce the $PSDefaultParameterValues again, but I’ll leave a quick explanation. This hash table allows us to instruct cmdlets and functions to use a default value for one of their parameters. Here’s a couple examples borrowed from the first two $PSDefaultParameterValues posts. To read the first two posts, follow the links at the bottom of this post. Both of these examples do the same thing, outside of the fact they’re written for different cmdlets.

$PSDefaultParameterValues.Add('Test-Connection:Count','1')
$PSDefaultParameterValues = @{'Get-Help:ShowWindow' = $true}

After our variable is set, anytime I use the Test-Connection cmdlet, it will include the -Count parameter with the parameter value of 1. Additionally, when I use Get-Help, it will always include the -ShowWindow parameter, without the need to enter it myself. The examples show how to set the variable both by using the Add method, and as a hash table — which is really all the variable is anyway.

I had a recent need to ensure the -Server parameter value on the Get-ADPrincipalGroupMembership cmdlet used the PDC Emulator. If you see the error: “The operation being requested was not performed because the user has not been authenticated, then you may need to ensure you’re using the PDCE when using this cmdlet, too. Anyway, I didn’t want to hard code the PDCE value in $PSDefaultParameterValues, so I tried something new, and you’re reading this today, because it worked. Here’s how I updated the $PSDefaultParameterValues variable to dynamically obtain the value it should use.

$PSDefaultParameterValues.Add('Get-ADPrincipalGroupMembership:Server',"$((Get-ADDomain).PDCEmulator)")
$PSDefaultParameterValues | Format-Table -AutoSize

Name                                  Value
----                                  -----
Get-ADPrincipalGroupMembership:Server DC01.mydomain.com

Now, whenever I run the Get-ADPrincipalGroupMembership cmdlet (inside the PowerShell session where the $PSDefaultParameterValues has been set), it’ll include the -Server parameter and the value of the PDCE — which ever server that is, and without the need to hard code its name. So yeah, we can use dynamic content in $PSDefaultParameterValues.

Part I: http://tommymaynard.com/quick-learn-give-a-parameter-a-default-value-2015
Part II: http://tommymaynard.com/quick-learn-give-a-parameter-a-default-value-part-ii-2015

Give a Parameter a Default Value (Part II)

Part I: http://tommymaynard.com/quick-learn-give-a-parameter-a-default-value-2015
Part III: http://tommymaynard.com/quick-learn-give-a-parameter-a-default-value-part-iii-2016

An old co-worker and friend contacted me last week. We hadn’t chatted since the last time I was interviewing for a job — a job I have now (well, pretty close anyway). I remember telling him I wanted a job that allowed me to work with Windows PowerShell. While he probably wasn’t surprised to hear this job did just that, he might have been, to hear I had started this site — a site using my name, and all about PowerShell. It’s a pretty serious commitment to associate your name with a technology, and continue to provide new content.

He mentioned to me that he wasn’t aware of the $PSDefaultParameterValues preference variable until he read this post. No joke, but it’s exciting to know that something I wrote was helpful for him. You see, this isn’t your average intelligence IT Pro, no, this is walking, talking IT genius. You know the kind — one of the ones you’d hire first, if you opened your own consulting business. In fact, during that same first chat, I discovered that he spoke at the Microsoft Higher-Education Conference in October 2014. He’s definitely doing something right.

As last weekend passed, I occasionally thought about that $PSDefaultParameterValues post and decided I should add something more to it, especially since I highlighted what I would consider to be the less used approach for populating this variable. First off, for those that haven’t read the previous post, the $PSDefaultParameterValues variable allows you to specify a default value for a cmdlet’s, or function’s, parameter(s).

For example, if I wanted the Get-Help cmdlet to always include the -ShowWindow parameter, then I can add that default value to the cmdlet like so:

PS C:\> $PSDefaultParameterValues
PS C:\> # Proof the variable is empty.
PS C:\> $PSDefaultParameterValues.Add('Get-Help:ShowWindow',$true)
PS C:\> $PSDefaultParameterValues

Name                           Value
----                           -----
Get-Help:ShowWindow            True

With this value set, every time we use the Get-Help cmdlet, it will include the -ShowWindow parameter, even though I don’t specifically enter it at the time the command is run. In the previous example, we use the .Add() method to add a key-value pair; however, I suspect that most people will actually be more likely to use a hash table to add the cmdlet and parameter, and its new, default parameter value. Here’s the same example as above using the hash table option.

PS C:\> $PSDefaultParameterValue
PS C:\> # Proof the variable is empty.
PS C:\> $PSDefaultParameterValues = @{'Get-Help:ShowWindow' = $true}
PS C:\> $PSDefaultParameterValues

Name                           Value
----                           -----
Get-Help:ShowWindow            True

Now for the reason I led with with .Add() method: If you use the hash table option above, and the variable is already populated, then it’s going to overwrite the value it’s already storing, unless we use the += assignment operator. Follow along in the next few examples under the assumption that $PSDefaultParameterValues, is already populated from the previous example.

PS C:\> $PSDefaultParameterValues

Name                           Value
----                           -----
Get-Help:ShowWindow            True

PS C:\> $PSDefaultParameterValues = @{'Get-ADUser:Server' = 'MyClosestDC'}
PS C:\> $PSDefaultParameterValues

Name                           Value
----                           -----
Get-ADUser:Server              MyClosestDC

In the example above, using the = assignment operator overwrote our Get-Help ShowWindow key-value pair, as it would with any populated variable. The idea here is that we either need to assign all the parameter default values at once (when using a hash table), or use the += assignment operator to append other key-value pairs. Here’s both ways:

PS C:\> $PSDefaultParameterValues
PS C:\> # Proof the variable is empty.
PS C:\> $PSDefaultParameterValues = @{'Get-Help:ShowWindow' = $true;'Get-ADUser:Server' = 'MyClosestDC'}
PS C:\> $PSDefaultParameterValues

Name                           Value
----                           -----
Get-ADUser:Server              MyClosestDC
Get-Help:ShowWindow            True

PS C:\> $PSDefaultParameterValues = $null
PS C:\> $PSDefaultParameterValues
PS C:\> # Proof the variable is empty.
PS C:\> $PSDefaultParameterValues = @{'Get-Help:ShowWindow' = $true}
PS C:\> $PSDefaultParameterValues += @{'Get-ADUser:Server' = 'MyClosestDC'}
PS C:\> $PSDefaultParameterValues

Name                           Value
----                           -----
Get-ADUser:Server              MyClosestDC
Get-Help:ShowWindow            True

That’s all there is to it. If you’re going to use a hash table and assign values to your $PSDefaultParameterValues at different times, then be sure to use the correct assignment operator, or use the .Add() method — it’s up to you. For me, I populate this variable in my profile, so overwriting it, is something in which I’m not concerned. Thanks for reading!

Get Some Help for Later Reading

I’m just starting to get my hands wet with Microsoft Lync. As I often do, I use the Windows PowerShell cmdlets to help learn more about a product; I did this same thing with Hyper-V. The unfortunate thing about the GUI (think, an MMC snap-in for instance), is that the menu options don’t always tell you exactly what that option is going to do, or its exact purpose. While the GUI can be unclear, PowerShell tells you exactly what a cmdlet does. With that knowledge, I’ve often been able to relate a cmdlet, and it’s purpose, to its respective menu option in the GUI.

I wanted to read though the Lync cmdlet’s help files, but only the cmdlet name and its synopsis. Here’s the command I ran to extract this information for later reading.

PS C:> Get-Command -Module Lync | Get-Help | Select-Object Name,Synopsis | Export-Csv -Path C:\LyncCmdlets.csv -NoTypeInfomation

The command above works this way: it returns all the cmdlets included in the Lync Module and sends (pipes) those to the Get-Help cmdlet. The Get-Help cmdlet pipes it’s results to Select-Object which filters the returned properties to just the Name and Synopsis from each cmdlets’ help file. At the end, those filtered results are sent to Export-Csv which creates a file I can read at my leisure.

Although there’s over 500 cmdlets, its safe to say that many of the nouns (the part after the dash (-)) will be the same across some of the cmdlets. That means that many of the Get-* cmdlets will have a partnering Set-* cmdlet. Get reads information and Set changes it. These nouns may also have a matching New-*, Remove-*, and possibly even a Test-* cmdlet. Now off to do some reading…

Determine if the Alias, or Function Name was Used

As a Windows PowerShell enthusiast, I am often thinking about PowerShell. Seems logical. Can I do this? What will happen if I do that? Why doesn’t this work!? Well, I had one of those thoughts recently. Can I determine if a function was called using an alias, or if it was called using the function name?

This thought occurred to me because of a change I considered adding to one of my functions. The idea was, that I wanted to prompt the user for confirmation to run a function (within the function), if an alias was used, and not prompt the user when the full function name was used. This lined up with the assumption that an alias could be accidentally entered more easily than the function name, and that we may want to take precautions when the alias was used.

My first consideration was to get the last command entered by the user, by using: (Get-History -Count 1).CommandLine. The problem with that “option,” is that the history isn’t updated until after the function has ended. This means that I wouldn’t know what was entered by the user while the function was running. Take a look at the example below. When I run the function Get-TMHistory the first time, nothing is displayed (in a fresh console), but something is displayed after the second run.

Function Get-TMHistory {
	Get-History -Count 1
}

PS C:\> Get-TMHistory
PS C:\> Get-TMHistory

  Id CommandLine
  -- -----------
   1 Get-TMHistory

I came up with a another idea. Let’s start by creating a new function called Get-TMHowCalled. In addition, we’ll need to create an alias for the function – let’s use ghc. I’ve included the New-Alias cmdlet’s -Force parameter in case there’s already an alias with that name. If there is, then New-Alias acts like Set-Alias, and updates the alias (instead of throwing an error). Note: This option could be problematic if it replaced ghc, and ghc was used for a different purpose.

New-Alias -Name ghc -Value Get-TMHowCalled -Force

Function Get-TMHowCalled {

}

The next thing to do is to construct the logic that will check and determine if the alias was used, or if the full function name was used. This is simple function: check, and echo what was entered by the user.

Function Get-TMHowCalled {
    If () {
        Write-Output -Verbose 'Alias was used.'
    } ElseIf () {
        Write-Output -Verbose 'Function name was used.'
    }
}

The secret here is the $MyInvocation automatic variable and its Line property. This stores what was entered, and so it can be used to determine how the function was called – by alias or by name. The best part, is that the variable is populated when the function is called and can, therefore, be queried inside the function. This variable can only be used in “scripts, functions, and script blocks.” You can read more about it using this command: Get-Help about_Automatic_Variables.

Function Get-TMHowCalled {
    If ($MyInvocation.Line -eq 'ghc') {
        Write-Output -Verbose 'Alias was used.'
    } ElseIf ($MyInvocation.Line -eq 'Get-TMHowCalled') {
        Write-Output -Verbose 'Function name was used.'
    }
}

Hope this proves to be helpful for someone. It might be for me.