How to determine if an EventLog already exists

问题:

I'm using the following line to create a new event log

new-eventlog -LogName "Visual Studio Builds" -Source "Visual Studio"

I want to run this every time, because if I run a build from a new computer, I'd still like to see the event logs.

The problem is that every time the script is run after the log is already created, it throws an error.

New-EventLog : The "Visual Studio" source is already registered on the "localhost" computer.
At E:\Projects\MyApp\bootstrap.ps1:14 char:13
+ new-eventlog <<<<  -LogName "Visual Studio Builds" -Source "Visual Studio"
    + CategoryInfo          : InvalidOperation: (:) [New-EventLog], InvalidOperationException
    + FullyQualifiedErrorId : Microsoft.PowerShell.Commands.NewEventLogCommand

Now I know that I can "search" for the event log

Get-EventLog -list | Where-Object {$_.logdisplayname -eq "Visual Studio Builds"} 

But now how do I determine if it exists?

回答1:

# Check if Log exists
# Ref: http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.exists(v=vs.110).aspx
[System.Diagnostics.EventLog]::Exists('Application');


# Ref: http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.sourceexists(v=vs.110).aspx
# Check if Source exists
[System.Diagnostics.EventLog]::SourceExists("YourLogSource");

回答2:

So I was on the right path with Get-EventLog.

Instead of just reading it, I stored it in a variable. Then I checked if the variable was null.

This has achieved what I was looking to do.

$logFileExists = Get-EventLog -list | Where-Object {$_.logdisplayname -eq "Visual Studio Builds"} 
if (! $logFileExists) {
    New-EventLog -LogName "Visual Studio Builds" -Source "Visual Studio"
}

回答3:

Check the Exists method:

[System.Diagnostics.EventLog]::Exists('Visual Studio Builds')

回答4:

if ([System.Diagnostics.EventLog]::SourceExists("Visual Studio") -eq $False) { New-EventLog -LogName "Visual Studio Builds" -Source "Visual Studio" }

回答5:

To simply check if exists:

$EventLogName = "LogName"
if ( !($(Get-EventLog -List).Log.Contains($EventLogName)))
{}

But to create the new one you'll need "As Administrator" privilege. To solve this I used to call a subprocess:

Start-Process -verb runAs powershell.exe  -ArgumentList "-file $PSScriptRoot\CreateLog.ps1" -wait

With simple CreateLog.ps1:

New-EventLog -LogName ScriptCheck -Source ScriptCheck
Write-EventLog –LogName ScriptCheck `
–Source ScriptCheck –EntryType Information –EventID 100 `
–Message "Start logging!"

回答6:

I think below approach could reduce the workload of filter with where

    try
    {
        Get-EventLog -LogName "Visual Studio Builds" -ErrorAction Ignore| Out-Null
    }
    catch {
        New-EventLog -LogName "Visual Studio Builds" -Source "Visual Studio"
    }

回答7:

Less complex:

 if (!(Get-Eventlog -LogName "Application" -Source "YourLog")){
      New-Eventlog -LogName "Application" -Source "YourLog"
 }

回答8:

$SourceExists = [System.Diagnostics.Eventlog]::SourceExists("XYZ")
if($SourceExists -eq $false){
    [System.Diagnostics.EventLog]::CreateEventSource("XYZ", "Application")
}

Just doing this is not enough. Even though you've created the event source, $SourceExists will always be false. I tested it also by running CreateEventSource then Remove-EventLog, and removing it failed. After creating an event source, you must write something to it. Append this after running CreateEventSource.

Write-EventLog -LogName "Application" -Source "XYZ" -EventID 0 -EntryType Information -Message "XYZ source has been created."

Thanks to https://stackoverflow.com/users/361842/johnlbevan pointing this out (in the comments).