How to Log with Timestamps in PowerShell

Who doesn’t like to have timestamps included their log files?

For me this is a requirement whenever I need to log. For obvious reasons, timestamp in logs will allow you to look back at what happened at a given date/time.

So let’s cut straight to the point, here are the 2 functions which I always include in all my scripts whenever I need logging.

function WriteLog {
    param ([String]$Msg)
    $TimeStamp = Get-Date -Format "dd/MM/yy HH:mm:ss"
    if ($Global:SaveLog) {
        if (-not (Test-Path "$Global:LogPath")) {
            New-Item -ItemType "directory" -Path "$Global:LogPath" -Force -Confirm:$false | Out-Null
        }
        $FileTimeStamp = Get-Date -Format "yyyyMMdd"
        $LogFileWithDate = ($Global:LogFileName.Replace(".log", "_$($FileTimeStamp).log"))
        Write-Output "[$TimeStamp] $Msg" | Out-File -FilePath "$($Global:LogPath)\$($LogFileWithDate)"  -Append
    }
    else {
        Write-Host "[$TimeStamp] $Msg"
    }
}


function CleanLogs {
    $Retention = (Get-Date).AddDays(-$($Global:LogRetentionInDays))
    Get-ChildItem -Path $Global:LogPath -Recurse -Force | Where-Object { $_.Extension -eq ".log" -and $_.CreationTime -lt $Retention } |
        Remove-Item -Force -Confirm:$false
}

To use these 2 functions, the following global variables must be defined:

1. $Global:SaveLog = $true | $false
2. $Global:LogPath = [string]C:\path\to\log\dir\
3. $Global:LogFileName = [string]my.log # must end with .log
4. $Global:LogRetentionInDays = [int] number

The WriteLog function can either write the log to STDOUT or write to a file. This depends on the $Global:SaveLog variable.

A separate log file is created for each day. The file will be suffixed with the current date like mylog_yyyyMMdd.log format.

The CleanLogs will purge/delete log files that are older than the retention period defined in days by the variable $Global:LogRetentionInDays

Example 1 - Logging to File

Here I will simply write out “Hello World!” to a log file.

function WriteLog {
    param ([String]$Msg)
    $TimeStamp = Get-Date -Format "dd/MM/yy HH:mm:ss"
    if ($Global:SaveLog) {
        if (-not (Test-Path "$Global:LogPath")) {
            New-Item -ItemType "directory" -Path "$Global:LogPath" -Force -Confirm:$false | Out-Null
        }
        $FileTimeStamp = Get-Date -Format "yyyyMMdd"
        $LogFileWithDate = ($Global:LogFileName.Replace(".log", "_$($FileTimeStamp).log"))
        Write-Output "[$TimeStamp] $Msg" | Out-File -FilePath "$($Global:LogPath)\$($LogFileWithDate)"  -Append
    }
    else {
        Write-Host "[$TimeStamp] $Msg"
    }
}

function CleanLogs {
    $Retention = (Get-Date).AddDays(-$($Global:LogRetentionInDays))
    Get-ChildItem -Path $Global:LogPath -Recurse -Force | Where-Object { $_.Extension -eq ".log" -and $_.CreationTime -lt $Retention } |
        Remove-Item -Force -Confirm:$false
}


$Global:SaveLog = $true
$Global:LogPath = "C:\Temp\Logs"
$Global:LogFileName = "my.log"  # must end with .log
$Global:LogRetentionInDays = 7

WriteLog "Hello World!"


# I always place this at the end of the script to ensure old logs are purged.
if ($Global:SaveLog) {
    WriteLog -Msg "Cleaning logs older than $($Global:LogRetentionInDays) days"
    CleanLogs
}

Note: $Global:LogPath doesn’t need to pre-exist, the function will create directory for you if is not already there . Using the example above, the script will create the “temp” and “log” folders on the first execution.

Now let’s check the output after running the code above.

PS C:\> Get-Content "C:\Temp\Logs\my_20211109.log"
[09/11/21 21:11:43] Hello World!
[09/11/21 21:11:43] Cleaning logs older than 7 days

Example 2 - Logging to Stdout

To log to Stdout, the $Global:SaveLog can be set to $false. Example:

PS C:\temp> .\logging_sample.ps1
[09/11/21 21:14:10] Hello World!

Note: When $Global:SaveLog is set to $false, the script will not attempt to delete old log files.

Conclusion

I often begin writing my scripts with $Global:SaveLog = $false. This allows me to quickly see the script output on my IDE terminal during development.

These 2 functions have been in many of my scripts over the years and I hope this can be useful for others who appreciates logging with timestamps :)

If you’ve made it this far, then I would like to say thank you and that you can also find this code on my GitHub page. I am open to all feedbacks and/or any pull requests if you think we can do better to improve on this.