Using script blocks within doubled quoted strings in PowerShell

While working on a script to convert an XML export of a new chat application to EML files for ingestion into my company’s compliance system (A task I’ve been doing a lot of over the past year or so), I came across an interesting use of variable usage in double quoted strings. One I was surprised I didn’t think of earlier.
Part of my script entailed providing options for grabbing various date ranges of the XML chat export from the provided REST API. I decided on the following options:

  • Full Export
  • This Date Forward
  • This Date Only

I normally use write-verbose statements partially as comment based help and a light version of logging for scripts like this. So when a non-full export was specified I wanted a write verbose statement like

Write-Verbose "Building REST URL for a $ExportType export using $ExportStartDate"

While a full export would be

Write-Verbose "Building REST URL for a $ExportType”

So I originally started with the following code

if ($ExportType -ne “Full”) {
Write-Verbose "Building REST URL for a $ExportType export using $ExportStartDate"
Else {
Write-Verbose "Building REST URL for a $ExportType export"

But then it dawned on me, I’ve done some expressions in double quoted strings before. A simple example would be

Write-host “Yesterday was $((Get-date -Hour 00 -Minute 00 -Second 00).adddays(-1).tostring())"

Could I do something a little more complex? Turns out I can! The following worked and could fit on one line

Write-Verbose "Building REST URL for a $ExportType export $(if($ExportType -ne “Full”) {"using $ExportStartDate"})"

Thinking about it some more. I wondered if I had a more complex statement as a script block. Could I pass that as well? Turns out I can!

[ScriptBlock]$CalculatedValue = {if($ExportType -ne “Full”) {"using $ExportStartDate"}}
Write-host "Building REST URL for a $ExportType export $(& $CaculdateValue)"
Write-host "Building REST URL for a $ExportType export $(Invoke-Command $CaculdateValue)"

Using either the call operator (&) or Invoke-Command I can execute a script block in a double quoted string. A fun trick I hope to use in the future to tighten up some code.

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