Log Helper writes to Event Log, console host or file depending on log source.

helper.logging.ps1

<#
    Logging functions.
#>

function logError([string]$logsrc, [string]$msg) {
    if ([String]::IsNullOrWhiteSpace($logsrc)) {
        write-log -msg $msg -level "ERROR"
    }
    elseif (@(".txt", ".log").Contains([System.IO.Path]::GetExtension($logsrc)) -eq $true) {
        write-log -msg $msg -level "ERROR" -file $logsrc
    }
    else {
        # write error msg to Application EventLog
        Write-EventLog -LogName Application -Source $logsrc -EventId 500 -EntryType Error -Message $msg -Category 0
    }
}

function logInfo([string]$logsrc, [string]$msg) {
    if ([String]::IsNullOrWhiteSpace($logsrc)) {
        write-log -msg $msg -level "INFO"
    }
    elseif (@(".txt", ".log").Contains([System.IO.Path]::GetExtension($logsrc)) -eq $true) {
        write-log -msg $msg -level "INFO" -file $logsrc
    }
    else {
        # write info msg to Application EventLog
        Write-EventLog -LogName Application -Source $logsrc -EventId 200 -EntryType Information -Message $msg -Category 0
    }
}

function logWarning([string]$logsrc, [string]$msg) {
    if ([String]::IsNullOrWhiteSpace($logsrc)) {
        Write-Host $msg -ForegroundColor Yellow
    }
    elseif (@(".txt", ".log").Contains([System.IO.Path]::GetExtension($logsrc)) -eq $true) {
        write-log -msg $msg -level "WARN" -file $logsrc
    }
    else {
        Write-EventLog -LogName Application -Source $logsrc -EventId 400 -EntryType Warning -Message $msg -Category 0
    }
}

# write log lines to a file
function write-log {
    [CmdletBinding()]
    param (
        [Parameter(Mandatory=$true)]
        [string]$msg,
        [Parameter(Mandatory=$false)]
        [ValidateSet("INFO","WARN","ERROR","DEBUG")]
        [string]$level = "INFO",
        [Parameter(Mandatory=$false)]
        [string]$file
    )

    $stamp = (get-date).ToString("yyyy/MM/dd HH:mm:ss")
    $line = "$stamp $level $msg"
    if ($file) {
        add-content $file -Value $line
    }

    # always write to console
    if ($level -eq "ERROR") {
      write-host $msg -ForegroundColor Red
    }
    elseif ($level -eq "WARN") {
      write-host $msg -ForegroundColor Yellow
    }
    else {
      write-host $msg
    }
}