Powershell Logging Module that incorporates logging to a file and to the Windows Event log in a structured manner. When using it from code it acts like a file stream when it really isn't.

Logging.psm1

<#
	.SYNOPSIS
		This module is to provide common functionality for logging within scripts
	.DESCRIPTION
		This module is to provide common functionality for logging within scripts.  This provides a consistent framework to be used
		universally across all PowerShell scripting platforms.
	.NOTES
		Version:		v1.2
    	Author: 		Jody Whitlock
    	Date:   		January 23, 2015
		LastModified: 	January 23, 2015		
		Purpose/Change:	Initial module development
#>

$global:CurrentOpenLog = ''
[string]$global:EventLogMessage = ''

#region Internal Functions
Function Get-CallingPath
{
	<#
		.SYNOPSIS
			Internal function to return the calling script's path
	#>
	if((Get-Variable MyInvocation).CommandOrigion -match "Internal")
	{
		$retVal = $PWD
	}
	else
	{
		$retVal = (Get-Variable MyInvocation).Value.PSScriptRoot
	}
	
	return $retVal
}

Function Get-LogNameFromScript
{
	<#
		.SYNOPSIS
			Internal function to return a log file name based on the calling script's name and the current date.
	#>
	$retVal = [IO.Path]::GetFileNameWithoutExtension((Get-Variable MyInvocation).Value.ScriptName)	
	if(!($retVal) -or ($retVal -match "Logging"))
	{
		$retVal = "CLI"
	}
	
	return "$($retVal)_$((Get-Date).ToString('MM-dd-yyyy')).log"
}

Function Get-EventSourceFromScript
{
	$retVal = [IO.Path]::GetFileNameWithoutExtension((Get-Variable MyInvocation).Value.ScriptName)
	if(!($retVal) -or ($retVal -match "Logging"))
	{
		$retVal = "CLI"
	}
	
	return $retVal
}

#endregion

Function Start-Log
{
	<#
		.SYNOPSIS
			Creates log file
		.DESCRIPTION
			Creates log file with path and name that is passed.  Once created, writes initial logging data
		.PARAMETER LogPath
			Path of where log is to be created. If this is ommitted, a log directory will be created under the calling scripts path
		.PARAMETER LogName
			Name of log file to be created.  If ommitted it will be the calling script name and current date appended.
		.OUTPUTS
			Log file name
		.EXAMPLE
			Start-Log -LogPath "C:\Windows\Temp" -LogName "Test_Script.log"
	#>
    
	[CmdletBinding()]
	Param
	(
		[Parameter(Mandatory=$false)]
		[string]$LogPath = "$(Get-CallingPath)\Log", 

		[Parameter(Mandatory=$false)]
		[string]$LogName = "$(Get-LogNameFromScript)"
	)
  
	Process
	{
		$sFullPath = $LogPath + "\" + $LogName
		
		$global:CurrentOpenLog = $sFullPath
		#Check if file exists and creates it if it doesn't
		If(!(Test-Path -Path $sFullPath))
		{
			if(!(Test-Path -Path $LogPath))
			{
				New-Item -Path $LogPath -ItemType Directory
			}
			New-Item -Path $LogPath -Name $LogName -ItemType File
		}

		Add-Content -Path $sFullPath -Value "***************************************************************************************************"
		Add-Content -Path $sFullPath -Value "Started processing at $([DateTime]::Now)."
		Add-Content -Path $sFullPath -Value "***************************************************************************************************"
		Add-Content -Path $sFullPath -Value ""

		$EventLogMessage += "Started processing at $([DateTime]::Now)."
		$EventLogMessage += "`n"
		
		#Write to screen for debug mode
		Write-Verbose "***************************************************************************************************"
		Write-Verbose "Started processing at $([DateTime]::Now)."
		Write-Verbose "***************************************************************************************************"
		Write-Verbose ""
		
		return "$($LogPath)\$($LogName)"
	}
}

Function Write-Log
{
	<#
		.SYNOPSIS
			Writes to a log file
		.DESCRIPTION
			Appends a new line to the end of the specified log file
		.PARAMETER LogPath
			Full path of the log file you want to write to. Example: C:\Windows\Temp\Test_Script.log
			If ommitted it will use the CurrentOpenLog file variable
		.PARAMETER LineValue
			Mandatory. The string that you want to write to the log
		.EXAMPLE
			Write-Log -LogPath "C:\Windows\Temp\Test_Script.log" -LineValue "This is a new line which I am appending to the end of the log file."
	#>
  
  	[CmdletBinding()]
	Param
	(
		[Parameter(Mandatory=$false)]
		[string]$LogPath = $global:CurrentOpenLog, 

		[Parameter(Mandatory=$true)]
		[string]$LineValue,
		
		[Parameter(Mandatory=$false)]
		[switch]$EventLog
	)
  
	Process
	{
		if($EventLog)
		{
			$EventLogMessage += $LineValue
			$EventLogMessage += "`n"
		}
		
		if($LogPath)
		{
			Add-Content -Path $LogPath -Value $LineValue
		}

		#Write to screen for debug mode
		Write-Verbose $LineValue
	}
}

Function Write-LogError
{
	<#
		.SYNOPSIS
			Writes an error to a log file
		.DESCRIPTION
			Writes the passed error to a new line at the end of the specified log file
		.PARAMETER LogPath
			Full path of the log file you want to write to. Example: C:\Windows\Temp\Test_Script.log
			If ommitted it will use the CurrentOpenLog file variable
		.PARAMETER ErrorDesc
			Mandatory. The description of the error you want to pass (use $_.Exception)
		.PARAMETER ExitGracefully
			Mandatory. Switch runs Log-Finish and then exits script
		.EXAMPLE
			Write-LogError -LogPath "C:\Windows\Temp\Test_Script.log" -ErrorDesc $_.Exception -ExitGracefully
	#>
  
	[CmdletBinding()]
	Param
	(
		[Parameter(Mandatory=$false)]
		[string]$LogPath = $global:CurrentOpenLog, 
		
		[Parameter(Mandatory=$true)]
		[string]$ErrorDesc, 
		
		[Parameter(Mandatory=$false)]
		[switch]$EventLog
		
	)
  
	Process
	{
		if($EventLog)
		{
			$EventLogMessage += $LineValue
			$EventLogMessage += "`n"
		}
		
		if($LogPath)
		{
			Add-Content -Path $LogPath -Value "Error: An error has occurred [$ErrorDesc]."
		}
		
		#Write to screen for debug mode
		Write-Verbose "Error: An error has occurred [$ErrorDesc]."

		if($EventLog)
		{
			Stop-Log -LogPath $LogPath -EventLog -EntryType Error
		}
		else
		{
			Stop-Log -LogPath $LogPath
		}
	}
}

Function Stop-Log
{
	<#
		.SYNOPSIS
			Write closing logging data & exit
		.DESCRIPTION
			Writes finishing logging data to specified log and then exits the calling script
		.PARAMETER LogPath
			Mandatory. Full path of the log file you want to write finishing data to. Example: C:\Windows\Temp\Test_Script.log
		.PARAMETER NoExit
			Optional. If this is set to True, then the function will not exit the calling script, so that further execution can occur
		.EXAMPLE
			Stop-Log -LogPath "C:\Windows\Temp\Test_Script.log"
		.EXAMPLE
			Stop-Log -LogPath "C:\Windows\Temp\Test_Script.log" -NoExit
	#>
  
	[CmdletBinding(DefaultParameterSetName="file")]
	Param
	(
		[Parameter(Mandatory=$false,
		ParameterSetName="file")]
		[string]$LogPath = $global:CurrentOpenLog, 
		
		[Parameter(Mandatory=$false,
		ParameterSetName="file")]
		[switch]$NoExit,
		
		[Parameter(Mandatory=$true,
		ParameterSetName="eventlog")]
		[Parameter(Mandatory=$false,
		ParameterSetName="file")]
		[switch]$EventLog,
		
		[Parameter(Mandatory=$false,
		ParameterSetName="eventlog")]
		[string]$EventLogName = "Windows PowerShell",
		
		[Parameter(Mandatory=$false,
		ParameterSetName="eventlog")]
		[System.Diagnostics.EventLogEntryType]$EntryType = "Information",
		
		[Parameter(Mandatory=$false,
		ParameterSetName="eventlog")]
		[int]$EventID = 1,
		
		[Parameter(Mandatory=$false,
		ParameterSetName="eventlog")]
		[string]$EventSource = (Get-EventSourceFromScript)
	)
  
	Process
	{		
		Add-Content -Path $LogPath -Value ""
		Add-Content -Path $LogPath -Value "***************************************************************************************************"
		Add-Content -Path $LogPath -Value "Finished processing at [$([DateTime]::Now)]."
		Add-Content -Path $LogPath -Value "***************************************************************************************************"

		#Write to screen for debug mode
		Write-Verbose ""
		Write-Verbose "***************************************************************************************************"
		Write-Verbose "Finished processing at [$([DateTime]::Now)]."
		Write-Verbose "***************************************************************************************************"
		
		if($EventLog)
		{
			$EventLogMessage += "Finished processing at [$([DateTime]::Now)]."
			$EventLogMessage += "`n"
			
			if(!($EventSource))
			{
				$EventSource = "PowerShell"
			}
							
			if(!(Get-EventLog -LogName $EventLogName -Source $EventSource -ErrorAction SilentlyContinue))
			{
				New-EventLog -LogName $EventLogName -Source $EventSource
			}
			
			Write-EventLog -LogName $EventLogName -EntryType $EntryType -EventId $EventID -Message $LineValue -Source $EventSource
		}
		
		#Exit calling script if NoExit has not been specified or is set to False
		If(!($NoExit))
		{
			Exit
		}    
	}
}

Export-ModuleMember -Function Start-Log
Export-ModuleMember -Function Write-Log
Export-ModuleMember -Function Write-LogError
Export-ModuleMember -Function Stop-Log