Logging made simple

Logging is perhaps not the first thing you think about when making small scripts that is only intended to be used by yourself, but the moment other people are involved, the probability of something going wrong is going up. And making scripts intended for others usually means the size and complexity goes up as well. At some point, you will get tired of feedback from others that are hard to debug, and wish you wrote logging into your script! What if logging was as simple as just adding a bunch of “Write-Log”‘s in your code? I’ll show you how.

I have created three logging functions that makes logging as easy as writing to the verbose stream. The first function (New-Log) you add one time, in the beginning of your script, and defines what kind of logging you want to do (it currently supports logging to file and to the Windows Event log), and some parameters.

Whenever you want to log something throughout your script, just use the second function (Write-Log). It works the same as all the other Write-* commands, except it has some different parameters relevant for logging. When writing to a file, it will automatically call the third function (Invoke-LogRotation) after each write, so you can keep some kind of control of your log(s).

Look at the help for New-Log and Write-Log for examples of use, and descriptions of the different parameters.

Even though I try to test out my functions thoroughly before releasing them, there are probably some bugs or stuff I haven’t thought about. So if you find anything wrong, or have any ideas for future improvement, let me know, ok?

Oh, and this is the first time I’m using a mutex (I found some excellent information about it from Boe Prox), so if I’m using it completely wrong, I’d appreciate you’d let me know!

function New-Log {
<#
.SYNOPSIS
Create a new log.
.DESCRIPTION
The New-Log function is used to create a new log file or Windows Event log. A log object is also created
and either saved in the global PSLOG variable (default) or sent to the pipeline. The latter is useful if
you need to write to different log files in the same script/function.
.EXAMPLE
New-Log '.\myScript.log'
Create a new log file called 'myScript.log' in the current folder, and save the log object in $global:PSLOG
.EXAMPLE
New-Log '.\myScript.log' -Header 'MyHeader – MyScript' -Append -Format 'CMTrace'
Create a new log file called 'myScript.log' if it doesn't exist already, and add a custom header to it.
The log format used for logging by Write-Log is the CMTrace format.
.EXAMPLE
$log1 = New-Log '.\myScript_log1.log'; $log2 = New-Log '.\myScript_log2.log'
Create two different logs that can be written to depending on your own internal script logic. Remember to
pass the correct log object to Write-Log!
.EXAMPLE
New-Log -EventLogName 'PowerShell Scripts' -EventLogSource 'MyScript'
Create a new log called 'PowerShell Scripts' with a source of 'MyScript', for logging to the Windows Event Log.
.NOTES
Author: Øyvind Kallstad
Date: 21.11.2014
Version: 1.0
#>
[CmdletBinding(DefaultParameterSetName = 'LogFile')]
param (
# Path to log file.
[Parameter(ParameterSetName = 'LogFile', Mandatory, Position = 0)]
[ValidateNotNullorEmpty()]
[string] $Path,
# Optionally define a header to be added when a new empty log file is created.
[Parameter(ParameterSetName = 'LogFile')]
[string] $Header,
# If log file already exist, append instead of creating a new empty log file.
[Parameter(ParameterSetName = 'LogFile')]
[switch] $Append,
# Maximum size of log file.
[Parameter(ParameterSetName = 'LogFile')]
[int64] $MaxLogSize = 1048576, # in bytes, default is 1048576 = 1 MB
# Maximum number of log files to keep. Default is 3. Setting MaxLogFiles to 0 will keep all log files.
[Parameter(ParameterSetName = 'LogFile')]
[ValidateRange(0,99)]
[int32] $MaxLogFiles = 3,
# The format of the log file. Valid choices are 'Minimal', 'PlainText' and 'CMTrace'.
# The 'Minimal' format will just pass the log entry to the log file, while the 'PlainText' includes meta-data.
# CMTrace format are viewable using the CMTrace.exe tool.
[Parameter(ParameterSetName = 'LogFile')]
[ValidateSet('Minimal','PlainText','CMTrace')]
[string] $Format = 'PlainText',
# Specifies the name of the event log.
[Parameter(ParameterSetName = 'EventLog', Mandatory)]
[string] $EventLogName,
# Specifies the name of the event log source.
[Parameter(ParameterSetName = 'EventLog', Mandatory)]
[string] $EventLogSource,
# Define the default Event ID to use when writing to the Windows Event Log.
# This Event ID will be used when writing to the Windows log, but can be overrided by the Write-Log function.
[Parameter(ParameterSetName = 'EventLog')]
[string] $DefaultEventID = '0',
# When UseGlobalVariable is True, the log object is saved in the global PSLOG variable, otherwise it's returned to the pipeline. Default value is True.
[Parameter()]
[switch] $UseGlobalVariable = $true
)
$elevated = $null
if ($PSCmdlet.ParameterSetName -eq 'EventLog') {
$logType = 'EventLog'
# when creating (and writing) to the event log, you need to run with elevated user rights
$windowsIdentity=[System.Security.Principal.WindowsIdentity]::GetCurrent()
$windowsPrincipal=new-object System.Security.Principal.WindowsPrincipal($windowsIdentity)
$adm=[System.Security.Principal.WindowsBuiltInRole]::Administrator
if ($windowsPrincipal.IsInRole($adm)) {
$elevated = $true
Remove-Variable Name Format,MaxLogSize,MaxLogFiles ErrorAction SilentlyContinue
# create new event log if needed
try {
if (-not([System.Diagnostics.EventLog]::SourceExists($EventLogName))) {
New-EventLog Source $EventLogSource LogName $EventLogName
Write-Verbose "Created new event log (Name: $($EventLogName), Source: $($EventLogSource))"
}
else {
Write-Verbose "$($EventLogName) exists, skip create new event log."
}
}
catch {
Write-Warning $_.Exception.Message
}
}
else {
Write-Warning 'When creating a Windows Event Log you need to run as a user with elevated rights!'
$elevated = $false
}
}
else {
$logType = 'LogFile'
# create new log file if needed
if((-not $Append) -or (-not(Test-Path $Path))){
try {
if($Header){
Set-Content Path $Path Value $Header Encoding 'UTF8' Force
}
else{
Set-Content Path $Path Value $null Encoding 'UTF8' Force
}
Write-Verbose "Created new log file ($($Path))"
}
catch{
Write-Warning $_.Exception.Message
}
}
}
# create log object
$logObject = [PSCustomObject] [Ordered] @{
LogType = $logType
LogFormat = $Format
Path = $Path
MaxLogSize = $MaxLogSize
MaxLogFiles = $MaxLogFiles
LogHeader = $Header
EventLogName = $EventLogName
EventLogSource = $EventLogSource
DefaultEventID = $DefaultEventID
Elevated = $elevated
}
# save logObject to a global variable
if($UseGlobalVariable){
$global:PSLOG = $logObject
}
# unless UseGlobalValiable is false, then return it to the pipeline instead
else{
Write-Output $logObject
}
}
function Write-Log {
<#
.SYNOPSIS
Write to the log.
.DESCRIPTION
The Write-Log function is used to write to the log. It is using the log object created by New-Log
to determine if it's going to write to a log file or to a Windows Event log.
.EXAMPLE
Write-Log 'Finished running WMI query'
Get the log object from $global:PSLOG and write to the log.
.EXAMPLE
$myLog | Write-Log 'Finished running WMI query'
Use the log object saved in $myLog and write to the log.
.EXAMPLE
Write-Log 'WMI query failed – Access denied!' -LogType Error -PassThru | Write-Warning
Will write an error to the event log, and then pass the log entry to the Write-Warning cmdlet.
.NOTES
Author: Øyvind Kallstad
Date: 21.11.2014
Version: 1.0
#>
[CmdletBinding()]
param (
# The text you want to write to the log.
[Parameter(Position = 0)]
[string] $LogEntry,
# The type of log entry. Valid choices are 'Error', 'FailureAudit','Information','SuccessAudit' and 'Warning'.
# Note that the CMTrace format only supports 3 log types (1-3), so 'Error' and 'FailureAudit' are translated to CMTrace log type 3, 'Information' and 'SuccessAudit'
# are translated to 1, while 'Warning' is translated to 2. 'FailureAudit' and 'SuccessAudit' are only really included since they are valid log types when
# writing to the Windows Event Log.
[Parameter()]
[ValidateSet('Error','FailureAudit','Information','SuccessAudit','Warning')]
[string] $LogType = 'Information',
# Event ID. Only applicable when writing to the Windows Event Log.
[Parameter()]
[string] $EventID,
# The log object created using the New-Log function. Defaults to reading the global PSLOG variable.
[Parameter(ValueFromPipeline)]
[ValidateNotNullorEmpty()]
[object] $Log = $global:PSLOG,
# PassThru passes the log entry to the pipeline for further processing.
[Parameter()]
[switch] $PassThru
)
try {
# get information from log object
$logObject = $Log
# translate event types to CMTrace format
if ($logObject.LogFormat -eq 'CMTrace') {
switch ($LogType) {
'Error' {$cmType = '3';break}
'FailureAudit' {$cmType = '3';break}
'Information' {$cmType = '1';break}
'SuccessAudit' {$cmType = '1';break}
'Warning' {$cmType = '2';break}
DEFAULT {$cmType = '1'}
}
}
# get invocation information
$thisInvocation = (Get-Variable Name 'MyInvocation' Scope 1).Value
# get calling script info
if(-not ($thisInvocation.ScriptName)){
$scriptName = $thisInvocation.MyCommand
$file = "$($scriptName)"
}
else{
$scriptName = Split-Path Leaf ($thisInvocation.ScriptName)
$file = "$($scriptName):$($thisInvocation.ScriptLineNumber)"
}
# get calling command info
$component = "$($thisInvocation.MyCommand)"
if ($logObject.LogType -eq 'EventLog') {
if($logObject.Elevated) {
# if EventID is not specified use default event id from the log object
if([system.string]::IsNullOrEmpty($EventID)) {
$EventID = $logObject.DefaultEventID
}
Write-EventLog LogName $logObject.EventLogName Source $logObject.EventLogSource EntryType $LogType EventId $EventID Message $LogEntry
}
else {
Write-Warning 'When writing to the Windows Event Log you need to run as a user with elevated rights!'
}
}
else {
# create a mutex, so we can lock the file while writing to it
$mutex = New-Object System.Threading.Mutex($false, 'LogMutex')
# handle the different log file formats
switch ($logObject.LogFormat) {
'Minimal' { $logEntryString = $LogEntry; break }
'PlainText' {
# when component and file are equal
if($component -eq $file){
$logEntryString = "$((Get-Date).ToString()) $($LogType.ToUpper()) [$($file)] $($LogEntry)"
}
# log entry when component and file are not equal
else{
$logEntryString = "$((Get-Date).ToString()) $($LogType.ToUpper()) [$($component) – $($file)] $($LogEntry)"
}
break
}
'CMTrace' {
$date = Get-Date Format 'MM-dd-yyyy'
$time = Get-Date Format 'HH:mm:ss.ffffff'
$logEntryString = "<![LOG[$LogEntry]LOG]!><time=""$time"" date=""$date"" component=""$component"" context="""" type=""$cmType"" thread=""$pid"" file=""$file"">"
break
}
}
# write to the log file
[void]$mutex.WaitOne()
Add-Content Path $logObject.Path Value $logEntryString
$mutex.ReleaseMutex()
# invoke log rotation if log is file
if ($logObject.LogType -eq 'LogFile') {
Invoke-LogRotation
}
# handle PassThru
if ($PassThru) {
Write-Output $LogEntry
}
}
}
catch {
Write-Warning $_.Exception.Message
}
}
function Invoke-LogRotation {
<#
.SYNOPSIS
Handle log rotation.
.DESCRIPTION
Invoke-LogRotation handles log rotation, using the log parameters defined in the log object.
This function is called within the Write-Log function so that log rotation are invoked after
each write to the log file.
.NOTES
Author: Øyvind Kallstad
Date: 21.11.2014
Version: 1.0
#>
[CmdletBinding()]
param (
# The log object created using the New-Log function. Defaults to reading the global PSLOG variable.
[Parameter(ValueFromPipeline)]
[ValidateNotNullorEmpty()]
[object] $Log = $global:PSLOG
)
try {
# get current size of log file
$currentSize = (Get-Item $Log.Path).Length
# get log name
$logFileName = Split-Path $Log.Path Leaf
$logFilePath = Split-Path $Log.Path
$logFileNameWithoutExtension = [System.IO.Path]::GetFileNameWithoutExtension($logFileName)
$logFileNameExtension = [System.IO.Path]::GetExtension($logFileName)
# if MaxLogFiles is 1 just keep the original one and let it grow
if (-not($Log.MaxLogFiles -eq 1)) {
if ($currentSize -ge $Log.MaxLogSize) {
# construct name of archived log file
$newLogFileName = $logFileNameWithoutExtension + (Get-Date Format 'yyyyMMddHHmmss').ToString() + $logFileNameExtension
# copy old log file to new using the archived name constructed above
Copy-Item Path $Log.Path Destination (Join-Path (Split-Path $Log.Path) $newLogFileName)
# set new empty log file
if ([string]::IsNullOrEmpty($Log.Header)) {
Set-Content Path $Log.Path Value $null Encoding 'UTF8' Force
}
else {
Set-Content Path $Log.Path Value $Log.Header Encoding 'UTF8' Force
}
# if MaxLogFiles is 0 don't delete any old archived log files
if (-not($Log.MaxLogFiles -eq 0)) {
# set filter to search for archived log files
$archivedLogFileFilter = $logFileNameWithoutExtension + '??????????????' + $logFileNameExtension
# get archived log files
$oldLogFiles = Get-Item Path "$(Join-Path Path $logFilePath ChildPath $archivedLogFileFilter)"
if ([bool]$oldLogFiles) {
# compare found log files to MaxLogFiles parameter of the log object, and delete oldest until we are
# back to the correct number
if (($oldLogFiles.Count + 1) -gt $Log.MaxLogFiles) {
[int]$numTooMany = (($oldLogFiles.Count) + 1) $log.MaxLogFiles
$oldLogFiles | Sort-Object 'LastWriteTime' | Select-Object First $numTooMany | Remove-Item
}
}
}
}
}
}
catch {
Write-Warning $_.Exception.Message
}
}

view raw
LogFunctions.ps1
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