Updates simple property files.

Set-PropertyValue.ps1

function Set-PropertyValue
{
    [CmdletBinding()]
    param($Path, $Key, $Value, $Separator='=', $Comment="# ", $Backup=$true)

    $ini        = Get-Content -Path $Path
    $newIniPath = [System.IO.Path]::GetTempFileName()
    $found      = $false

    $ini.Split("`n") |% {
        $line = $_.Trim()

        $iniLine = $line.Split('=')
        if ($iniLine.Count -eq 2 -and $iniLine[0].Trim() -like $Key)
        {
            $found = $true

            if ($iniLine[1].Trim() -notlike $Value)
            {
                if ($Comment.Length -gt 0)
                {
                    Write-Verbose -Message "Updated key [$($Key)] from [$($iniLine[1].Trim())] to [$($Value)]."
                    ($Comment + $line) | Add-Content -Path $newIniPath -Encoding Ascii
                }

                $line = $iniLine[0].Trim() + $Separator + $Value
            }
        }

        $line | Add-Content -Path $newIniPath -Encoding Ascii
    }

    if ($found -eq $false)
    {
        Write-Verbose -Message "New key [$($Key)] = [$($Value)]."
        $Key + $Separator + $Value | Add-Content -Path $newIniPath -Encoding Ascii
    }

    if ($Backup -eq $true)
    {
        $oldIniPath = $Path + '.BAK.' + (Get-Date).ToFileTimeUtc()
        Move-Item -Path $Path -Destination $oldIniPath -Force
        Write-Verbose -Message "Old INI has been saved as [$($oldIniPath)]."
    }

    Move-Item -Path $newIniPath -Destination $Path -Force
}