A PowerShell Parameter Puzzler


I ran across an interesting PowerShell behavior today thanks to a coworker (hi Matt!).

It involved a function with just a few arguments. When I looked at the syntax something looked off.

I am not going to recreate the exact scenario I found (because it involved a cmdlet written in C#), but I was able to recreate a similar issue using advanced functions.

So consider that you are entering a command and you see an intellisense prompt like this one:

You would rightfully assume that it had 3 parameters.

If you looked at the syntax using Get-Help (or the -? switch) you would see something strange:

Wait…where did the other 2 parameters go?

Using Get-Command get-Thing -syntax shows essentially the same result:

This was the kind of problem I ran into.  I was given a cmdlet, and when I looked at the syntax to see the parameters, I didn’t find the parameters I expected.  They were there, but they weren’t shown by Get-Command.

The “puzzle” is a bit less confusing when you see the code of the function:

function get-thing {
[CmdletBinding()]
Param(
  [Parameter(Position=0)]$parm1,
  [Parameter(Position=0)]$parm2,
  [Parameter(Position=0)]$parm3
)

#nothing to see here

}

The issue arose from the overlapping position modifiers on the parameters. When those are corrected the issue goes away.

Note: The original instance was a bit stranger. As I mentioned earlier, the cmdlet in question was written in C#. What really surprised me was that Get-Help and Get-Command showed different syntaxes. Get-Help showed all of the parameters, while Get-Command only showed the last one.

2 Comments

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