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CIM or WMI?

Working with WMI became a whole easier when PowerShell came on the scene. If you ever spent hours typing all of the Echo commands that were required with VBScript to produce output you’ll be aware of what I mean.  There are still a few awkward areas in the WMI cmdlets. One of the most awkward is date/time handling.

Consider looking for the last boot up time of your favourite computer:

£> Get-WmiObject -Class Win32_OperatingSystem | select -ExpandProperty LastBootUpTime
20140702083855.487133+060

 

That breaks down as year (2014), month (07), day (02), hour (08), minute (38), second (55) and fraction of a second (.487133). The +060 denotes the minutes offset from GMT (UTC if you prefer) – I’m in the UK on daylight saving time.  So, once you know how to read it the answer is understandable but not easy to work with.

The PowerShell team introduced a method on Get-WmiObject that will convert the date to a more understandable format:

 

£> $os = Get-WmiObject -Class Win32_OperatingSystem
£> $os.ConvertToDateTime($os.LastBootUpTime)

02 July 2014 08:38:55

 

You can also use the method in select-object or the format cmdlets by using a calculated field:

£> Get-WmiObject -Class Win32_OperatingSystem | Format-List PSComputerName, Caption, @{N='BootTime'; E={$_.ConvertToDate
Time($_.LastBootUpTime)}}


PSComputerName : RSSURFACEPRO2
Caption        : Microsoft Windows 8.1 Pro
BootTime       : 02/07/2014 08:38:55

 

There is an easier way – use the CIM cmdlets:

£> Get-CimInstance -ClassName Win32_OperatingSystem | select -ExpandProperty LastBootUpTime

02 July 2014 08:38:55

 

The automatic date conversion is more than sufficient incentive for me to use Get-CimInstance in preference to Get-WmiObject.

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