Generating log output using Windows PowerShell

I previously wrote a post in regards to streaming output to a log file synchronously in Windows PowerShell, which was required for a specific reason to lock the file during the script invocation and event message generation.

I have since created an advanced function to provide the ability to generate event messages to the console and/or a log file where the action is to append to a specified log file.

Firstly, we will specify the parameters for the advanced function:

LogFile -specify the location to create or append to an existing log file. If no log file is specified events are generated in the current Windows PowerShell session only. The parent directory name of the location is validated to determine if the location exists.

Message – specify a description of the event message.

Level – specify the severity of the event message, valid set of values are Info, Warning and Error. By default, the severity level of ‘Info’ is used.

	[CmdletBinding()]
	Param (
	[ValidateScript({Get-Item (Get-Item $_).DirectoryName})]
	[String]$LogFile = "",
	[Parameter(Mandatory=$True)]
	[String]$Message,
	[ValidateSet('Info','Error','Warning')]
	[String]$Level = "Info"
	)

view raw

Write-Log-AdvancedFunctionSnippet

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Based on the level parameter value we will use a conditional statement to generate the event message text. The message generates a timestamp in the SortableDateTimePattern format.

	Switch ($Level)
	{
	'Info' {$Event = ("" + (Get-Date -Format s) + ": INFORMATION: " + $Message + ".")}
	'Warning' {$Event = ("" + (Get-Date -Format s) + ": WARNING: " + $Message + ".")}
	'Error' {$Event = ("" + (Get-Date -Format s) + ": ERROR: " + $Message + ".")}
	}

view raw

Write-Log-SwitchConditionSnippet

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Now, we will be invoking the script block which generates the event message. Firstly, conditional logic determines if a log file has been specified and if so does the file exist and if not create the file.

Now we will output the event message to both the log file specified and to the current Windows PowerShell console session. If no log file has been specified the event message will be generated in the console session only.

	# Conditional logic to determine event generation method.
	If ($LogFile)
	{
	# Conditional logic to determine if the log file current exists in the location specified.
	If (!(Get-Item $LogFile -ErrorAction SilentlyContinue))
	{
	# Creates the log file in the location specified.
	New-Item $LogFile -Force -ItemType File \| Out-Null
	}
	# Generates events in the current Windows PowerShell session specified and the log file specified.
	Write-Host $Event
	Write-Output $Event \| Out-File -FilePath $LogFile -Append
	}
	Else
	{
	# Generates events in the current Windows PowerShell session.
	Write-Host $Event
	}