Invoke a script block with a temporary environment

Invoke-WithEnvironment.ps1

param(
    [Parameter(Position=0, Mandatory)]
    [hashtable]
    $private:Environment,

    [Parameter(Position=1, Mandatory)]
    $private:ScriptBlock
)

end {
    function ForEachKeyValuePair($hashtable, $scriptblock) {
        foreach ($entry in $hashtable.GetEnumerator()) {
            $key = $entry.Key
            $value = $entry.Value
            & $scriptblock
        }
    }

    ${@@private_backup@@} = @{}
    ForEachKeyValuePair $Environment { 
        if (Test-Path env:$key) {
            ${@@private_backup@@}[$key] = $value
        }
    }

    ForEachKeyValuePair $Environment { Set-Item env:$key $value }
    try {
        & $ScriptBlock
    } finally {
        ForEachKeyValuePair $Environment { Remove-Item env:$key }
        ForEachKeyValuePair ${@@private_backup@@} { Set-Item env:$key $value }
    }
}