Debugging Powershell

Debugging PowerShell can be extremely frustrating because it often turns into a session of debugging your own thought process. Often when I hit a PowerShell script issue I find myself feeling like everything is right and I’m just missing something basic. IMHO, this is because I spend the majority of my day programming in compiled languages and don’t completely come out of that box when I’m programming in PowerShell.

For instance the other day I added one of Lee Holme’s scripts to my default profile. The script is used to create a Generic object inside of PowerShell.

http://www.leeholmes.com/blog/CreatingGenericTypesInPowerShell.aspx

The syntax is very clean. It is the same as new-object but requires the additional type parameters.

$PS>new-genericobject Collections.Generic.List int
$PS>

The only problem was I couldn’t get the script to return an object. I tried a couple of operations like passing the output to get-member and seeing what exactly I was creating. I kept getting errors like “No object has been specified …”. My mind kept saying “It’s there, it’s non-null, why doesn’t it have any members!!!”.

Frustrated I turned to some internal aliases and eventually Lee helped me out. Nothing above is in error. The problem is PowerShell will unroll collection classes. In this case I’ve created an empty collection so there is nothing to output or pass to get-member. My issues is that I kept thinking it terms of compiled languages instead of PowerShell’s collection unrolling semantics (which I will add, I quite like).

Sadly any other object creating would have quickly lead me to this solution

C:\Users\jaredpar\winconfig\PowerShell> new-genericobject collections.generic.Ke
yValuePair int,int

                                    Key                                   Value
                                    ---                                   -----
                                      0                                       0

Another way to figure out this problem would be to bypass the collection unrolling in pipelines and directly specify the object to get-member.

C:\Users\jaredpar\winconfig\PowerShell> gm -inputobject $col
   TypeName: System.Collections.Generic.List`1[[System.Int32, mscorlib, Version
=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]
...