PowerShell 技能连载 - 在 PowerShell 中安全地使用 WMI(第 1 部分)

WMI (Windows Management Instrumentation) 是 Windows 操作系统的一部分并且广泛用于获取计算机系统的信息。PowerShell 之前引入了 Get-WmiObject 命令。在 PowerShell 3 中,增加了一个更现代的 Get-CimInstance 命令。

为了保持向后兼容,Windows PowerShell 始终保留了旧的 Get-WmiObject 命令,许多脚本开发者仍然在使用它而忽略了 Get-CimInstance。现在该是时候停止这个旧习惯因为 PowerShell Core (PowerShell 6, 7) 停止了对 Get-WmiObject 的支持。要确保脚本支持将来的 PowerShell 版本,您需要开始使用 Get-CimInstance 来代替 Get-WmiObject。

这刚开始看起来是微不足道的改变,实际上也确实是。对于简单的数据查询,您可能会通过 Get-CimInstance 来替换 Get-WmiObject:

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PS> Get-WmiObject -Class Win32_BIOS

SMBIOSBIOSVersion : 1.0.9
Manufacturer : Dell Inc.
Name : 1.0.9
SerialNumber : 4ZKM0Z2
Version : DELL - 20170001

PS> Get-CIMInstance -Class Win32_BIOS

SMBIOSBIOSVersion : 1.0.9
Manufacturer : Dell Inc.
Name : 1.0.9
SerialNumber : 4ZKM0Z2
Version : DELL - 20170001

请注意在 Get-CimInstance-Class 参数实际上改名为 -ClassName,但是由于 PowerShell 允许在参数名称唯一的情况下使用缩写,所以您无须改变参数名称。

然而,实际上 Get-WmiObject 和 Get-CimInstance 并不是 100% 兼容,并且您需要知道许多重要的区别,尤其是当您计划改变已有的脚本时。在这个迷你系列中,我们将看到最重要的实际差异。

让我们看看两个命令返回的信息。以下是一个查看返回属性的方法:

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# we are comparing this WMI class (feel free to adjust)
$wmiClass = 'Win32_OperatingSystem'

# get information about the WMI class Win32_OperatingSystem with both cmdlets
$a = Get-WmiObject -Class $wmiClass | Select-Object -First 1
$b = Get-CimInstance -ClassName $wmiClass | Select-Object -First 1

# dump the property names and add the property "Origin" so you know
# which property was returned by which command:
$aDetail = $a.PSObject.Properties | Select-Object -Property Name, @{N='Origin';E={'Get-WmiObject'}}
$bDetail = $b.PSObject.Properties | Select-Object -Property Name, @{N='Origin';E={'Get-CimInstance'}}

# compare the results:
Compare-Object -ReferenceObject $aDetail -DifferenceObject $bDetail -Property Name -PassThru |
Sort-Object -Property Origin

以下是执行结果:

Name                  Origin          SideIndicator
----                  ------          -------------
CimClass              Get-CimInstance =>
CimInstanceProperties Get-CimInstance =>
CimSystemProperties   Get-CimInstance =>
Qualifiers            Get-WmiObject   <=
SystemProperties      Get-WmiObject   <=
Properties            Get-WmiObject   <=
ClassPath             Get-WmiObject   <=
Options               Get-WmiObject   <=
Scope                 Get-WmiObject   <=
__PATH                Get-WmiObject   <=
__NAMESPACE           Get-WmiObject   <=
__SERVER              Get-WmiObject   <=
__DERIVATION          Get-WmiObject   <=
__PROPERTY_COUNT      Get-WmiObject   <=
__RELPATH             Get-WmiObject   <=
__DYNASTY             Get-WmiObject   <=
__SUPERCLASS          Get-WmiObject   <=
__CLASS               Get-WmiObject   <=
__GENUS               Get-WmiObject   <=
Site                  Get-WmiObject   <=
Container             Get-WmiObject   <=

结果显示 metadata 中有显著的区别。Get-WmiObject 总是返回再起属性 “__Server”(两个下划线)中进行查询的计算机的名称;而 Get-WmiObject 则是在 CimSystemProperties 中列出此信息:

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PS> $b.CimSystemProperties

Namespace ServerName ClassName Path
--------- ---------- --------- ----
root/cimv2 DESKTOP-8DVNI43 Win32_Process

PS> $b.CimSystemProperties.ServerName
DESKTOP-8DVNI43

不过,好消息是,类的特定属性并没有不同,因此这两个命令都返回有关操作系统、BIOS 或您所查询的其它内容的相同基本信息。这一行返回相同的属性:

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Compare-Object -ReferenceObject $aDetail -DifferenceObject $bDetail -Property Name -IncludeEqual -ExcludeDifferent -PassThru |  Sort-Object -Property Origin | Select-Object -Property Name, SideIndicator


Name SideIndicator
---- -------------
ProcessName ==
ParentProcessId ==
PeakPageFileUsage ==
PeakVirtualSize ==
PeakWorkingSetSize ==
Priority ==
PrivatePageCount ==
ProcessId ==
QuotaNonPagedPoolUsage ==
QuotaPagedPoolUsage ==
QuotaPeakNonPagedPoolUsage ==
PageFileUsage ==
QuotaPeakPagedPoolUsage ==
PSComputerName ==
ReadTransferCount ==
SessionId ==
Status ==
TerminationDate ==
ThreadCount ==
UserModeTime ==
VirtualSize ==
WindowsVersion ==
WorkingSetSize ==
ReadOperationCount ==
WriteOperationCount ==
PageFaults ==
OtherOperationCount ==
Handles ==
VM ==
WS ==
Path ==
Caption ==
CreationClassName ==
CreationDate ==
CSCreationClassName ==
CSName ==
Description ==
OtherTransferCount ==
CommandLine ==
ExecutionState ==
Handle ==
HandleCount ==
InstallDate ==
KernelModeTime ==
MaximumWorkingSetSize ==
MinimumWorkingSetSize ==
Name ==
OSCreationClassName ==
OSName ==
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