Powershell - “清除项目变量:"与“删除变量" [英] Powershell - "Clear-Item variable:" vs "Remove-Variable"

问题描述

在运行时将文本临时存储在 powershell 变量中时，从内存中删除不再需要的变量内容的最有效方法是什么?

When storing text temporarily in powershell variables at runtime, what is the most efficient way of removing a variables contents from memory when no longer needed?

我同时使用了 Clear-Item variable: 和 Remove-Variable 但是使用后者从内存中删除某些东西的速度与使用以前?

I've used both Clear-Item variable: and Remove-Variable but how quickly does something get removed from memory with the latter vs nulling the memory contents with the former?

我应该更清楚地说明我为什么要问.

I should have made it a little clearer why I am asking.

我正在为一堆应用程序虚拟机自动化 RDP 登录(应用程序不作为服务运行，外包开发人员，长话短说).

I am automating RDP login for a bunch of application VMs (application doesn't run as a service, outsourced developers, long story).

因此，我正在开发(基本完成)一个脚本来将启动会话分组到每个 VM.

So, I am developing (largely finished) a script to group launch sessions to each of the VMs.

想法是存储凭据的脚本函数使用 read-host 提示输入主机名，然后 get-credentials 获取域/用户/密码.

Idea is that the script function that stores credentials uses read-host to prompt for hostname then get-credentials to pick up domain/user/password.

然后使用 256 位密钥(存储凭证并运行组启动的机器/用户唯一的运行时密钥)从安全字符串转换通行证.

The pass is then converted from secure-string using 256-bit key (runtime key unique to machine/user that stored the creds and runs the group launch).

VM 名称、域、用户和加密通行证存储在一个文件中.启动会话时，读取详细信息，解密密码，将详细信息传递给 cmdkey.exe 以存储该 VM 的 \generic:TERMSRV 凭据，清除明文传递变量，将 mstsc 启动到该主机，几秒钟后从 Windows 凭据存储中删除凭据.(如果我将密码作为明文以外的任何内容传递给 cmdkey.exe，则 RDP 会话将收到不正确的凭据或没有凭据).

The VMs name, domain, user and encrypted pass are stored in a file. When launching a session, the details are read in, password decrypted, details passed to cmdkey.exe to store \generic:TERMSRV credential for that VM, clear plaintext pass variable, launch mstsc to that host, a few seconds later remove the credential from windows credential store. (If I passed password to cmdkey.exe as anything other than plaintext, the RDP session would either receive incorrect or no credentials).

因此，问题是，我需要密码以明文形式存在于内存中尽可能短的时间.

So, hence the question, I need the password In plaintext to exist in memory for as short a time as possible.

为了让安全人员满意，脚本本身是 aes256 加密的，并且带有自己的 ps 主机的 c# 包装器读取、解密和运行脚本，因此在运行它的机器上没有明文源.(文件共享上的加密源非常有效，我有一个终止开关，可以简单地用另一个显示此应用程序已被禁用的消息替换加密脚本)

To keep security guys happy, the script itself is aes256 encrypted and a c# wrapper with its own ps host reads, decrypts and runs the script, so there is no plaintext source on the machine that runs this. (Encrypted source on a file share so effectively I have a kill switch, can simply replace encrypted script with another displaying a message that this app has been disabled)

推荐答案

您可以使用秒表来获取命令行开关的执行时间.我认为这两个 cmdlet 之间并没有真正的时差.我通常使用删除项目"，因为在我看来最好删除完整的变量.

You can use a stopwatch to get the execution time for the commandlets. I think there is not really a time difference between these two cmdlets. I´m using normally "Remove-Item" because in my eyes it´s better to remove a variable complete.

$a = "TestA"
$b = "TestB"
$c = "TestC"
$d = "TestD"

$time = New-Object system.Diagnostics.Stopwatch  

Start-Sleep 1
$time.Start() 
$time.Stop()
$system = $time.Elapsed.TotalMilliseconds
Write-Host "Stopwatch StartStop" $system
$time.Reset()

Start-Sleep 1
$time.Start() 
Clear-Item Variable:a
$time.Stop()
$aTime = $time.Elapsed.TotalMilliseconds - $system
Write-Host "Clear-Item in " $aTime
$time.Reset()

Start-Sleep 1
$time.Start() 
Remove-Variable b
$time.Stop()
$bTime  = $time.Elapsed.TotalMilliseconds - $system
Write-Host "Remove-Variable in " $bTime
$time.Reset()

Start-Sleep 1
$time.Start() 
Clear-Item Variable:c
$time.Stop()
$cTime = $time.Elapsed.TotalMilliseconds - $system
Write-Host "Clear-Item in " $cTime
$time.Reset()

Start-Sleep 1
$time.Start() 
Remove-Variable d
$time.Stop()
$dTime  = $time.Elapsed.TotalMilliseconds - $system
Write-Host "Remove-Variable in " $dTime
$time.Reset()

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