Powershell Watch-Command

Watch-Command.ps1

##
## Author   : Roman Kuzmin
## Synopsis : Watch one screen of commands output repeatedly
## Modified : 2006.11.06
## Source   : http://nightroman.wordpress.com/2006/09/26/watch-command-ps1-watch-commands-output-repeatedly/?replytocom=43#respond
##
## Modified : 2012.11.15 - tgmayfield - Support for System.Double wait times, output a title string similar to *nix watch command
##
## -Command_: script block which output is being watched
## -Seconds : refresh rate in seconds
##
## *) Commands should not operate on console.
## *) Tabs are simply replaced with spaces.
## *) * indicates truncated lines.
## *) Empty lines are removed.
## *) Ctrl-C to stop.
##

function Watch-Command
{
	param([scriptblock]$Command_ = {Get-Process}, [double]$Seconds = 2)

	$private:ms = [int]($Seconds * 1000)
	$private:sb = New-Object System.Text.StringBuilder
	$private:w0 = $private:h0 = 0
	for(;;) {

		# invoke command, format output data
		$private:n = $sb.Length = 0
		$private:w = $Host.UI.RawUI.BufferSize.Width
		$private:h = $Host.UI.RawUI.WindowSize.Height-1
		$private:title = [System.String]::Format("Every {0:N1}s: {1}", $Seconds, $Command_)

		[void]$sb.EnsureCapacity($w*$h)
		.{
			$private:dateDisplay = [System.DateTime]::Now.ToString("G")
			[void]$sb.Append($title)
			[void]$sb.Append("   ($dateDisplay)")
			[void]$sb.AppendLine()
			[void]$sb.AppendLine()
			++$n
			++$n
			& $Command_ | Out-String -Stream | .{process{
				if ($_ -and ++$n -le $h) {
					$_ = $_.Replace("`t", ' ')
					if ($_.Length -gt $w) {
						[void]$sb.Append($_.Substring(0, $w-1) + '*')
					}
					else {
						[void]$sb.Append($_.PadRight($w))
					}
				}
			}}
		}>$null

		# fill screen
		if ($w0 -ne $w -or $h0 -ne $h) {
			$w0 = $w; $h0 = $h
			Clear-Host; $private:origin = $Host.UI.RawUI.CursorPosition
		}
		else {
			$Host.UI.RawUI.CursorPosition = $origin
		}
		Write-Host $sb -NoNewLine
		$private:cursor = $Host.UI.RawUI.CursorPosition
		if ($n -lt $h) {
			Write-Host (' '*($w*($h-$n)+1)) -NoNewLine
		}
		elseif($n -gt $h) {
			Write-Host '*' -NoNewLine
		}
		$Host.UI.RawUI.CursorPosition = $cursor
		Start-Sleep -Milliseconds $ms
	}
}