PowerShell Write-Eventlog

PowerShell Write-Eventlog Cmdlet

PowerShell's Write-Eventlog is one of the most difficult cmdlets to master.  The problem is that we are asking a script to mimic how the operating system or an application writes to eventlog.  For that to be successful we need to understand valid source and EventIDs. 

PowerShell Write-Eventlog Topics

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Firstly, Let Us Have a Refresher with Get-Eventlog

PowerShell Eventlog -List

Pre-requisites:
Visit Microsoft's site and download the correct version of PowerShell for your operating system.

So that you can focus on the properties of the message, I suggest that you become familiar with Get-Eventlog before graduating to Write-Eventlog.

Our first task is to list the logs on your machine.  My idea is to see which logs are present, and then to select a log to write messages:

# PowerShell script to list the event logs.
Get-Eventlog -List

Learning Points

Note 1: -List is correct, please note that you do need that dash.

Action Point:  Launch the Windows Eventvwr and then visit the actual logs to check that the result of the above script matches what you see in the Event Viewer's GUI.  As a general tactic I encourage you have the Windows GUI open to compare with the PowerShell scripts.

PowerShell Write-Eventlog Preparation

  • Not only must the eventlog you specify exist, but also the -Source application must be able to write to the log. 
  • If you have Microsoft Vista, Windows 7, Server 2008 or later, launch Windows PowerShell with the "Run as administrator" option.

Write-Eventlog Example Using Windows PowerShell's Own Log

There is no business case, or technical reason for using this script, my idea is merely to provide a working example.  Thus feel free to alter the properties and parameters.  I am sure there will be many failures before you achieve just the script for your task.

# Example of Write-Eventlog to 'Windows PowerShell' log
Clear-Host
Write-Eventlog -ComputerName LocalHost -Logname 'Windows PowerShell' `
-Source PowerShell -EventID 600 -EntryType Warning `
-Message "Guy is at work."
# Optional Section to display the newly written event
[System.Threading.Thread]::CurrentThread.CurrentCulture = `
New-Object "System.Globalization.CultureInfo" "en-US"
Get-WinEvent -LogName 'Windows PowerShell' -MaxEvents 10

Note 2:
-ComputerName is optional. I suggest that you omit and thus start with the local machine.
-Logname must exist.  You could try Windows PowerShell.
-EventID use a number you can see in the log, just to get started.
-EntryType defaults to 'Application'.
-Message - I suggest something with your name in it, just so you can see if it worked.

Note 3: I recommend PowerShell splatting to format your parameters.

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Write-Eventlog Example Using the Application Log

# PowerShell Write-Eventlog to Application log.
Clear-Host
Write-Eventlog  -Logname 'Application' -Source 'Application' `
-EventID 1000 -EntryType Information -Message "Guy is at work."
Show-Eventlog
#Invoke-Item "C:\Windows\system32\eventvwr.msc"

Note 4: I omitted the -computerName parameter.Write-EventLog

Note 5: Originally, I appended Invoke-Item so that you can look for the new item in the Event Viewer; it helps me to have the appropriate Windows GUI open when I run my PowerShell scripts.  Then I discovered PowerShell has cmdlet for this job called: Show-Eventlog

Note 6: To make this work for real you need a clear rational of what you want to write into the log - Application, PowerShell or other.  My aim is just to give you examples of the mechanics and to make you aware of all the parameters that you must consider.

Get-Eventlog Displays New Messages

Key point, Get-Eventlog is followed by the name of the log, in this case 'Application'.

# PowerShell script to find Error messages in the Application eventlog.
Get-EventLog Application -Newest 10 | where {$_.EntryType -Match "Information"}

Learning Points

Note 7: You could simplify the script further and just type:
Get-EventLog Application

Note 8: Each word, and indeed every symbol, has deep meaning to PowerShell.  (|) pipes the output of the first clause into the 'Where' statement.  As a result the output is filtered so that you see only error messages, and not information or warning messages.

Note 9:  PowerShell supports a whole family of conditional statements, for example, -Like, -Contains, or even plain -eq (Equals), but for this job, I chose -Match.  See more on PowerShell conditional statements.

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More Research into PowerShell's Write-Eventlog

Trusty Twosome (Get-Help and Get-Member)

Whenever you discover a new PowerShell command, it benefits from being surveyed with what I call the 'Trusty Twosome'.  In this instance, if you research a Verb-Noun command with Get-Help and Get-Member, then you are sure to unearth new scripting possibilities. To see what I mean try:

Get-Help (For Parameter Research)

# Investigate PowerShell Write-Eventlog -parameters
Clear-Host
Get-Help Write-Eventlog -full

Get-Help confirms that starting in PowerShell v2.0 Write-Eventlog supports the -ComputerName parameter, thus you can interrogate the Eventlogs on network machines.

Other names of logs that you can substitute for 'System' are: Application, Security and even PowerShell itself has a log.  Windows Server is likely to have yet more logs, for example, Directory Service and DNS Server.

Get-Member (To Display Properties)

# Investigate PowerShell Get-Eventlog Properties
Clear-Host
Write-Eventlog system | Get-Member -MemberType property

Note 10: You could omit the -MemberType property parameter and thus display methods.

Discover Other Members of the PowerShell Eventlog Family

# Find more Eventlog cmdlets
Clear-Host
Get-Command -Noun eventlog

Name
-------------------
Clear-EventLog
Get-EventLog
Limit-EventLog
New-EventLog
Remove-EventLog
Show-EventLog
Write-EventLog   (also Write-Progress)

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Get-WinEvent Cmdlet

Get-WinEvent is the successor to Get-Eventlog.  Remember that to test this cmdlet you need PowerShell v 2.0.

Take the opportunity to learn more about PowerShell while you undertake the worthwhile task of examining the various event logs, for example, system, windows or DNS.

See more PowerShell Write-Eventlog examples ยป

Summary of PowerShell Write-Eventlog Scripts

If I were you, I would master one the simpler cmdlets such as Get-Eventlog before graduating to Write-Eventlog.  Once you start scripting real-life task, take the trouble to study parameters such as -Source and -EventID.

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See more PowerShell examples to read, write and list Windows event logs

PowerShell Home   • Get-Eventlog   • EventVwr -list  • Clear-WinEvent Function   • Remote Eventlog

PowerShell Limit-Eventlog   • Windows 8 Event Viewer   • Get-WinEvent  • Log Event Manager

Write-Eventlog (Basic)   • PowerShell Write-Eventlog (Adv)  • PowerShell Clear-Eventlog

Please email me if you have a better example script. Also please report any factual mistakes, grammatical errors or broken links, I will be happy to correct the fault.

 

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