只输出额外的文本，例如

Just output the extra text e.g.

(Get-Content $fileName) | 
    Foreach-Object {
        $_ # send the current line to output
        if ($_ -match "pattern") 
        {
            #Add Lines after the selected pattern 
            "Text To Add"
        }
    } | Set-Content $fileName

您可能不需要额外的n"，因为 PowerShell 将为您行终止每个字符串.

You may not need the extra ``n` since PowerShell will line terminate each string for you.