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

You need to group the sub-expressions you want to preserve (i.e. put them between parentheses) and then reference the groups via the variables $1 and $2 in the replacement string. Try something like this:

$regexA = '( TEST=[A-Za-z]+)14(\d\d)$'

Get-ChildItem '*.txt' | ForEach-Object {
    $c = (Get-Content $_.FullName) -replace $regexA, '${1}16$2' -join "`r`n"
    [IO.File]::WriteAllText($_.FullName, $c)
}