Advanced Windows PowerShell Scripting Video Training

Advanced Windows PowerShell Scripting Video Training
Advanced Windows PowerShell Scripting Video Training

Monday, November 19, 2012

Use the difference between event log time stamps to decide if you need to take action

Today I am on a long flight back to Indianapolis after a week of training at Microsoft. Being the geek that I am I decided to take a quick look at PowerShell.org to see if anybody in the community was having issues that I could help with before we took off. One community member needed to be able to tell if two events were being recorded more than 2 hours apart. If so, she wanted an action to take place.

I used the Subtract Method of the System.DateTime object that is given to you in the TimeCreated property of an individual event log to resolve this. In the below function, I have it extract the first two events that match the criteria in $EventHash. I then take the first returned event and subtract the second events time from the first and then look for the TotalHours property. If it is greater than the number of hours specified when the function was called, it returns True. If not, it returns False.  It also has a built in safety.  If 1 or less events are returned, the function defaults to False.

 
Function Get-EventTimeSpan
{
Param (
[Parameter(Mandatory
=$True)]$Hours
)
# Specify the criteria for your event here.
$EventHash = @{LogName = "System"; ID = 1014}

# Recover the first two events from the event log that matches
# the criteria in the $EventHash data.
$EventData = Get-WinEvent -FilterHashtable $EventHash -MaxEvents 2

# Verify that at least two events were recovered from the log.
# If there are less than 2 events recovered, Execute the ELSE
# Statement. The Else statement should execute code if only one
# or less events are found.
If ($EventData.Count -eq 2)
{
If ((($EventData[0].TimeCreated).Subtract(($EventData[1].TimeCreated)).TotalHours) -lt $Hours)
{
# Return $False if the time between events is less than the
# number of hours specified in $Hours.
Write-Output $False
}
Else
{
# Return $False if the time between events is greater than the
# number of hours specified in $Hours.
Write-Output $True
}
}
# End: If ($EventData.Count -lt 2)
Else
{
#If there are less than 2 events in the event log, return $False
Write-Output $False
}
# End: Else Statement for If ($EventData.Count -lt 2)



}
# ---- End Function Get-EventTimeSpan ---------------------------------------


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