Groovy Jenkins powershell pipe not working - powershell

Question

I want to replace some text in a file after Jenkins does its build step.
I have the code below in my post build step.
powershell.exe -Command(Get-Content "./PublishedWebsites/app.config") |
Foreach-Object {$_.replace({{MyDummValue}}, "${env.BUILD_NUMBER}")} |
Set-Content "./PublishedWebsites/app.config"
The first part works (Get-Content "./PublishedWebsites/app.config") up until the pipe ("|").
After the pipe it throws an error that Foreach-Object is not recognized by an internal or external command.
I am thinking it has something to do with the escape sequence and the syntax.
So I have tried this as well
"""powershell.exe -Command(Get-Content "./PublishedWebsites/app.config") |
Foreach-Object {$_.replace({{MyDummValue}}, "${env.BUILD_NUMBER}")} |
Set-Content "./PublishedWebsites/app.config"""
Then for some reason jenkins is trying to evaluate the $_.replace({{MyDummValue}} before the post build step is even reached and gives me the error of 'Cannot get property replace on null object'
So I am at a loss. All I want to do is on a post build step, rename a value in a file with the Build Number.

Answer 1

When calling PowerShell (or other) scripts from Groovy, always use single-quoted (or triple-single-quoted) string literals for the script. With double-quoted (or triple-double-quoted) strings, Groovy tries to interpolate the string, so you'd have to escape $ as \$, to use it literally. While this is just a nuisance, double-quoted strings are also prone to script injection, where a pipeline user might run arbitrary PowerShell scripts, when pipeline parameters are interpolated by Groovy within the script.
Another mistake: the value {{MyDummValue}} isn't quoted.
Also, I don't know why you are calling powershell.exe explicitly. Use the powershell step instead:
post {
always { // or one of the other available sections
powershell '''
Get-Content "./PublishedWebsites/app.config" |
Foreach-Object {$_.replace("{{MyDummValue}}", $env:BUILD_NUMBER)} |
Set-Content "./PublishedWebsites/app.config"
'''
}
}