Writing Output to Log Files in PowerShell Script

Logging to simple text files is a convenient way to track all actions performed by a PowerShell script.  Such a log file is useful for debugging script errors and reviewing executed actions. In this article, we’ll explore different ways to log the output of PowerShell scripts by writing to text log files.

Redirecting PowerShell Terminal Output to a Log File

By default, PowerShell command results are displayed in the console. To redirect the output of a PowerShell command to a text file, use one of the following methods:

• Redirection using >> operator
• Use Add-Content to add some plain text to the end of the log file
• Use Out-File to write formatted text to a file

Here are examples of three different commands that add a new line with the output of a PowerShell command to the log file.

Write-Output "Files are successfully created in $env:computername" >> C:\PS\Logs\TestLog.txt
Add-Content -Path C:\PS\Logs\TestLog.txt -Value "Files are successfully created in $env:computername"
"Files are successfully created in $env:computername" | Out-File -FilePath C:\PS\Logs\TestLog.txt –Append
# The -Append parameter is used to add data to a file without overwriting existing data.

In all cases, the commands add a new line to a TXT file with the text you have specified.

The main disadvantages of using such logging commands:

• The current timestamp of when the event occurred is not logged
• Every time you want to write something to the log, you have to call a somewhat complex PowerShell construct
• The path to the log file is hardcoded

Adding a Logging Function to a PowerShell Script

If you prefer a more convenient logging method, the easiest way is to add a separate function to the PowerShell script that writes the data that it receives to a log file with a timestamp.

You can create a function as shown below:
$Logfile = "C:\PS\Logs\$($env:computername)posh.log"
function WriteLog
{
Param ([string]$LogString)
$Stamp = (Get-Date).toString("yyyy/MM/dd HH:mm:ss")
$LogMessage = "$Stamp $LogString"
Add-content $LogFile -value $LogMessage -Encoding UTF8
}

Now, call the WriteLog function when you want to log something to a text file.

WriteLog "The script is run"
WriteLog "Calculating..."
Start-Sleep 20
WriteLog "The script is successfully executed"

Now, the log file contains the timestamp when the new line (log entry) was added.

Now, you can replace the console output via Write-Host command in all PS1 scripts with WriteLog.

Automatic PowerShell Logging with Start-Transcript

PowerShell has another built-in transcript feature that writes all the commands that run in the console and their results to a text log file. To start recording commands in the current PowerShell session, run the command:

Start-Transcript

This will create a text log file in the Documents directory of the current user’s profile (the filename is specified in the console).

Transcript started, output file is C:\Users\user\Documents\PowerShell_transcript.DESKTOP-P2FHTKQ.+IzDgZiN.20210908163729.txt

Run some PowerShell commands that print the results to the console. For example, let’s list the running processes, services, and get the AD replication status:

Write-Host "Transcript logging"
Get-Process| where-object {$_.WorkingSet -GT 500000*1024}|select processname,@{l="Used RAM(MB)"; e={$_.workingset / 1mb}} |sort "Used RAM(MB)" –Descending
Get-Service | Where-Object {$_.status -eq 'Running'}
Get-ADReplicationFailure -Target mun-dc01

Stop logging for the current PowerShell session:

Stop-Transcript

Then, open the transcript log file.

This text log contains the complete history of the PowerShell commands that were executed, along with any results output to the console.

The Start-Transcript and Stop-Transcript commands can be used in PowerShell scripts to natively log all actions and results.

The “Turn on PowerShell Transcription” GPO option (Computer Configuration –> Administrative Templates –> Windows Components –> Windows PowerShell) enables the automatic logging of all PowerShell commands and their output on the computer. After updating the GPO settings on the computer, a separate text log file will be created for each running powershell.exe (pwsh.exe) process, and all PowerShell commands and their outputs will be logged.