Use Powershell to replace subsection of regex result

Question

Using Powershell, I know how to search a file for a complicated string using a regex, and replace that with some fixed value, as in the following snippet:

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Answer 1

Here's an example using a scriptblock delegate (sometimes called an evaluator):

$regex = [regex]'( TEST=\D+)14(\d{2})\s*$'
$evaluator = { '{0}16{1}' -f $args[0].Groups[1..2] }
filter set-number { $regex.Replace($_, $evaluator) }

foreach ($file in Get-ChildItem  "*.txt")
 {
   ($file | get-content) | set-number | Set-Content $file.FullName
 }

It's arguably more complex than the -replace operator, but lets you use powershell operators to construct the replacement text, so you can do anything you can put in a script block.