TailScLog.ps1

# Tail Sitecore log files, even when using rolling log files
# ==========================================================
# 1) Copy this file into your App_Data folder or set the logFolder parameter to point to the Sitecore logs folder.
# 2) Run it in Powershell
# 3) View the log messages as they appear (even if the worker process recycles)
param (
    [string]$logFolder = ".\\logs\\", 
    [string]$filter = "log.*",
    [int]$tailAmount = 20
)

$global:currentFile = $null
$global:reader = $null
$global:skip = 0
$global:executionCount = 0

Function ResolveCurrentFile
{
	Param([string] $baseDir, [string] $fileFilter)

	# Find the most recent log file
	return (Get-ChildItem -Path $baseDir -Filter $fileFilter | Sort LastWriteTime | Select -last 1).FullName
}

Function SetCurrentFile
{
	Param([string] $newFile, [int] $tailLineCount)
	if($newFile -eq $global:currentFile)
	{
		# If there is no newer file, just stop processing here and keep going with the previous one
		return;
	}

	$global:currentFile = $newFile

	# Write a message to indicate that there is a new log file
	Write-Host "===== Opening file $newFile =====" -ForegroundColor Black -BackgroundColor White

	# Close existing reader (if any)
	if($global:reader)
	{
		$global:reader.Close();
		$global:reader = $null;
	}

	$global:skip = 0

	# Open a file stream and setup a reader to read lines of text from it
	$fileStream = New-Object -TypeName System.IO.FileStream -ArgumentList $global:currentFile, ([System.IO.FileMode]::Open), ([System.IO.FileAccess]::Read), ([System.IO.FileShare]::ReadWrite)
	$global:reader = New-Object -TypeName System.IO.StreamReader -ArgumentList $fileStream

	# Count the number of lines, so that we know how to use the tail number
	while(!($global:reader.ReadLine() -eq $null))
	{
		$global:skip = $global:skip + 1
	}

	# Reset the filestream position so we can start reading "for real"
	$fileStream.Position = 0

	# Calculate the number of lines to skip on the next read
	$global:skip = $global:skip - $tailLineCount
}

Function StartReading()
{
	while($True)
	{
		# Keep a number of executions, so that we know how often to check for changes
	    $global:executionCount = $global:executionCount + 1;

		# Read the next line in the file
		$line = $global:reader.ReadLine()

		if($global:skip -gt 0)
		{
			# Tail implies that you skip lines until you can read the "tail" amount of lines from the file
			$global:skip = $global:skip - 1
		}
		else
		{
			if(!($line -eq $null))
			{
				if(![string]::IsNullOrWhiteSpace($line))
				{
					# Colorize the message if there is info on the severity
					if($line -like '* FATAL *')
					{
						Write-Host $line -ForegroundColor Red -BackgroundColor White
					}
					elseif($line -like '* ERROR *')
					{
						Write-Host $line -ForegroundColor Red
					}
					elseif($line -like '* WARN *')
					{
						Write-Host $line -ForegroundColor Yellow
					}
					else
					{
						Write-Host $line
					}
				}
			}
			else
			{
				# Don't continuously read from the filesystem, take a break
				Start-Sleep -Milliseconds 200

				# On every 10th execution, check if there is a newer log file
				if($global:executionCount % 10 -eq 0)
				{
					$newFile = ResolveCurrentFile $logFolder $filter
					SetCurrentFile $newFile $tailAmount
					$global:executionCount = 0
				}
			}
		}
	}
}

try
{
	# Resolve the most recently changed log file
	$newFile = ResolveCurrentFile $logFolder $filter

	# Setup a file stream and count the number of lines
	SetCurrentFile $newFile $tailAmount

	# Start an endless loop that occasionally monitors for new files
	StartReading
}
catch
{
	# If anything goes wrong, let us know
	Write-Host $_.Exception.Message
}
finally
{
	# Ensure that the reader is closed, so that any file locks are released
	if($global:reader)
	{
		$global:reader.Close();
		$global:reader = $null;
	}
}