Simple function to write to a log file

Write-Log.ps1

<#
Write-Log.ps1
20181027 - 4dilio
Simple function to write to a log file.
You MUST define $Log in your script.
#>

function Write-Log {
  [CmdletBinding()]
  param(
      [Parameter()]
      [ValidateNotNullOrEmpty()]
      [string]$Message,

      [Parameter()]
      [ValidateNotNullOrEmpty()]
      [ValidateSet('Information','Warning','Error')]
      [string]$Severity = 'Information'
  )

  $Time = (Get-Date -Format 'MM-dd-yy HH:mm:ss')

  # Check if $Log is defined and exists;
  # if not, create it.
  If ($Log -eq $null) {
    $Log = "LogOutput.txt"
  }
  ElseIf ( -Not (Test-Path -LiteralPath $Log)) {
    New-Item -ItemType File -Force -Path $Log > $null
  }

  # Note: You MUST specify $Log in your script
  Write-Output "$Time - [$Severity] - $Message" |
    Out-File $Log -Append
  
  # Truncate log file to avoid filling up drive
  $TruncLog = Get-Content -Tail 1000 $Log
  $TruncLog | Out-File $Log
}