If you are not aware, a developer version of Windows 8 was released at the build conference. For the purpose of this blog I will use a specific tag (3.0 Win 8 Developer Build) for these posts so that I can remove and clean them up once PowerShell 3.0 is RTM.
I was looking at the new variables with dir variable: in PowerShell 3.0 and one caught my eye: $PSDefaultParameterValues
Interesting. The first thing to do is inspect it. The following shows the trail of that inspection:
PS C:\Users\toenuff.Win8> $PSDefaultParameterValues
_____________________________________________________________________________________________________
PS C:\Users\toenuff.Win8> $PSDefaultParameterValues.gettype()
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True False DefaultParameterDictionary System.Collections.Hashtable
_____________________________________________________________________________________________________
PS C:\Users\toenuff.Win8> $PSDefaultParameterValues |gm
TypeName: System.Management.Automation.DefaultParameterDictionary
Name MemberType Definition
---- ---------- ----------
Add Method System.Void Add(System.Object key, System.Object value)
ChangeSinceLastCheck Method bool ChangeSinceLastCheck()
Clear Method System.Void Clear()
Clone Method System.Object Clone()
Contains Method bool Contains(System.Object key)
ContainsKey Method bool ContainsKey(System.Object key)
ContainsValue Method bool ContainsValue(System.Object value)
CopyTo Method System.Void CopyTo(array array, int arrayIndex), System.Vo...
Equals Method bool Equals(System.Object obj)
GetEnumerator Method System.Collections.IDictionaryEnumerator GetEnumerator(), ...
GetHashCode Method int GetHashCode()
GetObjectData Method System.Void GetObjectData(System.Runtime.Serialization.Ser...
GetType Method type GetType()
OnDeserialization Method System.Void OnDeserialization(System.Object sender)
Remove Method System.Void Remove(System.Object key)
ToString Method string ToString()
Item ParameterizedProperty System.Object Item(System.Object key) {get;set;}
Count Property System.Int32 Count {get;}
IsFixedSize Property System.Boolean IsFixedSize {get;}
IsReadOnly Property System.Boolean IsReadOnly {get;}
IsSynchronized Property System.Boolean IsSynchronized {get;}
Keys Property System.Collections.ICollection Keys {get;}
SyncRoot Property System.Object SyncRoot {get;}
Values Property System.Collections.ICollection Values {get;}
I’m not sure what DefaultParameterDictionary is, but it’s derived from a hash table. So, what happens when you try to set some values in there?
PS C:\Users\toenuff.Win8> $PSDefaultParameterValues.tome = 'blah'
The key 'tome' has an invalid format. The key must consist of one command name and one parameter name
separated only by a colon (CommandName:ParameterName). The command name and/or the parameter name can
be enclosed in individual quotation marks ("CommandName":"ParameterName"), but the entire key cannot be
enclosed in quotation marks. To disable the $PSDefaultParameterValues feature, set the key/value pair
to Disabled=$true.
At line:1 char:1
+ $PSDefaultParameterValues.tome = 'blah'
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvalidOperation
JACKPOT!!!! We learn that the key name needs to be command:parametername and we learn that we can disable this feature by setting $PSDefaultParameterName.Disabled = $true.
It looks like we can set default parameter values now. Just choose the cmdlet along with parameter name as follows:
$PSDefaultParameterValues.('Invoke-Command:Credential') = (get-credential)
Now every time I run Invoke-Command it uses the credentials I specified earlier without having to ever use the -Credential parameter again. Will this feature make the final cut? I’m not sure. It does have security implications. What if a rogue module developer attacked you by setting default parameters for a cmdlet? Then again, a rogue module developer could do a lot worse than this. If nothing else, there is certainly practical joke material here when we start modifying our friend’s profiles on April 1st. I’m curious. What do you think we can do with this feature? What cmdlets are screaming for this to be used in your profile?
Here’s my list:
- Every PowerCLI command Confirm equal to $false
- Perhaps a function that wraps invoke-command and Enter-PSSession so that every time it is run it sets the default value to the last computer you connected to.
- Get-ChildItem:Force = $true
- Write-Progress – I hate having to remember all of the parameters when I really just want to update one bit of activity and the percentage on the bar.
- Send-MailMessage – From, Subject, Body, SMTPServer – The beautiful thing is that you can set all of the defaults and override with the parameter as needed
- Default servers for your AD cmdlets of choice
- $PSDefaultParameterValues.(‘Select-Object:Property’) = ‘*’ ; This would let you do things like get-process |select #saving you two keystrokes over select *
- Verbose in any cmdlet that you think is appropriate
- Export-CSV and Out-File : Encoding = ASCII
- ErrorAction = SilentlyContinue – I put this one last as a joke. Please people, don’t do this
What cmdlets and parameters do you think this makes sense for? Please feel free to leave comments to discuss.
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I’ve been waiting for that for a long while. 🙂