pipe loop to out-gridview and clear grid on every loop? - powershell

Question

I'm just wondering if I can clear Out-Gridview on every loop like I can in the console:
while (1) { ps | select -first 5; sleep 1; clear-host }
Unfortunately this doesn't clear out-gridview every time:
& { while (1) { ps | select -first 5; sleep 1; clear-host } } | out-gridview

Answer 1

Clear-Host clears the display of the host, which is the console window's content in a regular PowerShell console.
By contrast, Out-GridView is a separate GUI window, over which PowerShell offers no programmatic display once it is being displayed.
Notably, you can neither clear no refresh the window's content after it is displayed with the initial data.
The best approximation of this functionality is to close the old window and open a new one with the new data in every iteration - but note that this will be visually disruptive.
In the simplest case, move the Out-GridView into the loop and call it with -Wait, which requires you to close it manually in every iteration, however:
# NOTE: Doesn't move to the next iteration until you manually close the window.
while (1) { ps | select -first 5 | Out-GridView -Wait }
This answer shows how to implement an auto-closing Out-GridView window, but it is a nontrivial effort - and with a sleep period as short as 1 second it will be too visually disruptive.
Ultimately, what you're looking for is a GUI version of the Unix watch utility (or, more task-specifically, the top utility).
However, since you're not looking to interact with the Out-GridView window, there's little benefit to using Out-GridView in this case.
Instead, you could just spawn a new console window that uses Clear-Host to display the output in the same screen position periodically:
The following defines helper function Watch-Output to facilitate that:
# Simple helper function that opens a new console window and runs
# the given command periodically, clearing the screen beforehand every time.
function Watch-Output ([scriptblock] $ScriptBlock, [double] $timeout = 1) {
$watchCmd = #"
while (1) {
Clear-Host
& { $($ScriptBlock -replace '"', '\"') } | Out-Host
Start-Sleep $timeout
}
"# #'
Start-Process powershell.exe "-command $watchCmd"
}
# Invoke with the command of interest and a timeout.
Watch-Output -ScriptBlock { ps | Select -First 5 } -Timeout 1
Note that this will still flicker every time the window content is refreshed.
Avoiding that would require substantially more effort.
The PowerShellCookbook module offers the sophisticated Watch-Command cmdlet, which not only avoids the flickering but also offers additional features.
The big caveat is that - as of version 1.3.6 - the module has several cmdlets that conflict with built-in ones (Format-Hex, Get-Clipboard, New-SelfSignedCertificate, Send-MailMessage, Set-Clipboard), and the only way to import the module is to allow the module's commands to override the built-in ones (Import-Module PowerShellCookbook -AllowClobber).