Why doesn't $hash.key syntax work inside the ExpandString method?

Question

The following Powershell script demonstrates the issue:

$hash = @{\'a\' = 1; \'b\' = 2}
Write-Host $hash[\'a\']        # => 1
Write-Host $hash.a                   


        

Answer 1

I was trying to store text that prompts the user in a text file. I wanted to be able to have variables in the text file that are expanded from my script.

My settings are stored in a PSCustomObject called $profile and so in my text I was trying to do something like:

Hello $($profile.First) $($profile.Last)!!!

and then from my script I was trying to do:

$profile=GetProfile #Function returns PSCustomObject 
$temp=Get-Content -Path "myFile.txt"
$myText=Join-String $temp
$myText=$ExecutionContext.InvokeCommand.ExpandString($myText) 

which of course left me with the error

Exception calling "ExpandString" with "1" argument(s): "Object reference not set to an instance of an object."

Finally I figured out I only needed to to store the PSCustomObject values I want in regular old variables, change the text file to use those instead of the object.property version and everything worked nicely:

$profile=GetProfile #Function returns PSCustomObject 
$First=$profile.First
$Last=$profile.Last
$temp=Get-Content -Path "myFile.txt"
$myText=Join-String $temp
$myText=$ExecutionContext.InvokeCommand.ExpandString($myText) 

And in the text I changed to

Hello $First $Last!!!