Functions/Start-ScriptLogger.ps1

<#
    .SYNOPSIS
    Start the script logger inside the current PowerShell session.

    .DESCRIPTION
    Start the script logger inside the current PowerShell session. By starting
    the logger, a global log configuration for the current PowerShell session
    will be set. This configuration is customizable with the available
    paramters.
    With the format parameter, the logfile format can be defined. The format
    definition will be used to call the System.String.Format() method. The
    following values are used as arguments:
    {0} Timestamp as datetime value.
    {1} NetBIOS computer name.
    {2} Current session username.
    {3} Log entry level.
    {4} Message.

    .INPUTS
    None.

    .OUTPUTS
    ScriptLogger.Configuration. Configuration of the script logger instance.

    .EXAMPLE
    PS C:\> Start-ScriptLogger
    Initialize the logger with default values

    .EXAMPLE
    PS C:\> Start-ScriptLogger -Path 'C:\test.log' -Format '{3}: {4}' -Level 'Verbose' -SkipEventLog -HideConsoleOutput
    Log all message with verbose level or higher to the log file but skip the
    event log and the consule output. In addition, use a custom format for the
    log file content.

    .NOTES
    Author : Claudio Spizzi
    License : MIT License

    .LINK
    https://github.com/claudiospizzi/ScriptLogger
#>


function Start-ScriptLogger
{
    [CmdletBinding(SupportsShouldProcess = $true)]
    [System.Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSAvoidGlobalVars', '')]
    param
    (
        # The path to the log file.
        [Parameter(Mandatory = $false)]
        [ValidateScript({(Test-Path -Path (Split-Path -Path $_ -Parent))})]
        [System.String]
        $Path = (Join-Path -Path ([System.IO.Path]::GetTempPath()) -ChildPath 'PowerShell.log'),

        # This parameter defines, how the log output will be formated.
        [Parameter(Mandatory = $false)]
        [ValidateScript({$_ -f (Get-Date), $Env:ComputerName, $Env:Username, 'Verbose', 'Message'})]
        [System.String]
        $Format = '{0:yyyy-MM-dd} {0:HH:mm:ss} {1} {2} {3,-11} {4}',

        # The event log level. All log messages equal to or higher to the level
        # will be logged. This is the level order: Verbose, Information, Warning
        # and Error.
        [Parameter(Mandatory = $false)]
        [ValidateSet('Verbose', 'Information', 'Warning', 'Error')]
        [System.String]
        $Level = 'Verbose',

        # Define the encoding which is used to write the log file. The possible
        # options are the same as on the used Out-File cmdlet.
        [Parameter(Mandatory = $false)]
        [ValidateSet('Unicode', 'UTF7', 'UTF8', 'UTF32', 'ASCII', 'BigEndianUnicode', 'Default', 'OEM')]
        [System.String]
        $Encoding = 'Default',

        # Do not write the log messages into the log file. By default, all
        # messages are written to the specified or default log file.
        [Parameter(Mandatory = $false)]
        [Switch]
        $NoLogFile,

        # Skip the event log output. By default, all log messages will be
        # written into the "Windows PowerShell" event log.
        [Parameter(Mandatory = $false)]
        [Switch]
        $NoEventLog,

        # Hide the PowerShell console output. By default, all log messages are
        # shown on the console.
        [Parameter(Mandatory = $false)]
        [Switch]
        $NoConsoleOutput
    )

    # Create an empty log file, if it does not exist
    if (-not (Test-Path -Path $Path))
    {
        New-Item -Path $Path -ItemType File | Out-Null
    }

    # Only work with absolute path, makes error handling easier
    $Path = (Resolve-Path -Path $Path).Path

    if ($PSCmdlet.ShouldProcess('ScriptLogger', 'Start'))
    {
        Write-Verbose "Enable script logger with log file '$Path'"

        # Define global variable for the logging
        $Global:ScriptLogger = New-Object -TypeName PSObject -Property @{
            Enabled       = $true
            Path          = $Path
            Format        = $Format
            Level         = $Level
            Encoding      = $Encoding
            LogFile       = -not $NoLogFile.IsPresent
            EventLog      = -not $NoEventLog.IsPresent
            ConsoleOutput = -not $NoConsoleOutput.IsPresent
        }
        $Global:ScriptLogger.PSTypeNames.Insert(0, 'ScriptLogger.Configuration')

        # Return logger object
        return $Global:ScriptLogger
    }
}