Advanced Windows PowerShell Scripting Video Training

Advanced Windows PowerShell Scripting Video Training
Advanced Windows PowerShell Scripting Video Training

Wednesday, April 13, 2016

Positional Parameters and Switch Parameters Odd Behavior

So here is a neat one from my class today.  I love it when someone comes in and looks at a problem from a different perspective.  Take a look at these two lines of code:
Get-ChildItem C:\Windows -Recurse

Get-ChildItem -Recurse C:\Windows

They both work!  This is what caught my attention. Look at the same command with all of the parameters named.
Get-ChildItem -Path C:\Windows -Recurse

In the first example, we are using the –Path parameter as positional.  Here is the information form the help file:
PS C:\> Get-Help Get-ChildItem -Parameter Path

-Path <String[]>
    Specifies a path to one or more locations. Wildcards are permitted. The
    default location is the current directory (.).
   
    Required?                    false
    Position?                    1
    Default value                Current directory
    Accept pipeline input?       true (ByValue, ByPropertyName)
    Accept wildcard characters?  true

You can see it is in position 1.  In the second example, we placed in position 2, but it still worked! OK, time to play.  Right off the bat, we suspected that SWITCH parameters do not consume a position so we tested this theory.
Get-ChildItem -Recurse -Directory C:\Windows

It worked.  Both –Recurse and –Directory are SWITCH parameters.  So to play with it further, I decided to add the –Filter parameter which is in position 2.
PS C:\> Get-ChildItem -Path C:\Windows -Filter "System*"


    Directory: C:\Windows


Mode                LastWriteTime         Length Name                         
----                -------------         ------ ----                         
d-----       10/30/2015  12:24 AM                System                       
d-----        4/12/2016   8:54 AM                System32                     
d-----       10/30/2015   2:07 AM                SystemApps                   
d-----       10/30/2015  12:24 AM                SystemResources              
-a----        8/22/2013   6:25 AM            219 system.ini                   


Adding in the switch parameters also worked.
Get-ChildItem -Recurse -Directory -Path C:\Windows -Filter "System*"

Using –Path and –Filter as positional parameters after the switch parameters did not work.
PS C:\> Get-ChildItem -Recurse  -Directory C:\Windows "System*"
Get-ChildItem : Second path fragment must not be a drive or UNC name.
Parameter name: path2
At line:1 char:1
+ Get-ChildItem -Recurse  -Directory C:\Windows "System*"
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (C:\:String) [Get-ChildItem], A
   rgumentException
    + FullyQualifiedErrorId : DirArgumentError,Microsoft.PowerShell.Commands.G
   etChildItemCommand

However using them with the switch parameters after the positional parameters do work.
PS C:\> Get-ChildItem C:\Windows "System*" -Recurse  -Directory


    Directory: C:\Windows


Mode                LastWriteTime         Length Name                          
----                -------------         ------ ----                         
d-----       10/30/2015  12:24 AM                System                       
d-----        4/12/2016   8:54 AM                System32                     
d-----       10/30/2015   2:07 AM                SystemApps                   
d-----       10/30/2015  12:24 AM                SystemResources              


When I named one of the positional parameters, it worked.
Get-ChildItem -Recurse  -Directory -Path C:\Windows "System*"

Get-ChildItem -Recurse  -Directory C:\Windows -Filter "System*"

From this quick test run, the best that I can come up with is that when you use switch parameters before positional parameters, only 1 positional parameter will work.  All others need to be named.








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