文字列の連結/書式設定を行おうとしていますが、すべてのパラメーターを最初のプレースホルダーに入れています。
コード
function CreateAppPoolScript([string]$AppPoolName, [string]$AppPoolUser, [string]$AppPoolPass)
{
    # Command to create an IIS application pool
    $AppPoolScript = "cscript adsutil.vbs CREATE ""w3svc/AppPools/$AppPoolName"" IIsApplicationPool`n"
    $AppPoolScript += "cscript adsutil.vbs SET ""w3svc/AppPools/$AppPoolName/WamUserName"" ""$AppPoolUser""`n"
    $AppPoolScript += "cscript adsutil.vbs SET ""w3svc/AppPools/$AppPoolName/WamUserPass"" ""$AppPoolPass""`n"
    $AppPoolScript += "cscript adsutil.vbs SET ""w3svc/AppPools/$AppPoolName/AppPoolIdentityType"" 3"
    return $AppPoolScript
}
$s = CreateAppPoolScript("name", "user", "pass")
write-host $s
出力
cscript adsutil.vbs CREATE "w3svc/AppPools/name user pass" IIsApplicationPool
cscript adsutil.vbs SET "w3svc/AppPools/name user pass/WamUserName" ""
cscript adsutil.vbs SET "w3svc/AppPools/name user pass/WamUserPass" ""
cscript adsutil.vbs SET "w3svc/AppPools/name user pass/AppPoolIdentityType" 3