How to get/download all WSP in SharePoint Using Powershell Script?

$dirName = ""
Write-Host Exporting solutions to $dirName
foreach ($solution in Get-SPSolution)
{
$id = $Solution.SolutionID
$title = $Solution.Name
$filename = $Solution.SolutionFile.Name
Write-Host "Exporting ‘$title’ to …\$filename" -nonewline
try {
$solution.SolutionFile.SaveAs("$dirName\$filename")
Write-Host " – done" -foreground green
}
catch
{
Write-Host " – error : $_" -foreground red
}
}