Truncated output when running Powershell command in a loop
I wrote the following function as a rudimentary way of implementing basic functionality of the *nix watch command within Powershell:
function watch {
Param(
[Parameter(Mandatory=$true)][string]
$command,
[Parameter(Mandatory=$false)][int]
$n = 2
)
while($true) {
clear
Write-Output (iex $command)
sleep $n
}
}
When working with cmdlets that return Powershell objects, I get strange behavior. For example if I run `watch 'get-command ls', on the first iteration I get the following formatted output of the object:
CommandType Name Version Source
----------- ---- ------- ------
Alias ls -> Get-ChildItem
But on the second and subsequent iterations, it truncates the object property headers (and any description above it in certain other commands):
Alias ls -> Get-ChildItem
I'm curious as to why this behavior happens, and how I can make the output identical to the first iteration for all subsequent iterations. I am running this in Powershell 5.1 on Windows 10.
I think it's because you're mashing up Write-Output which writes to the pipeline, and clear which is properly named Clear-Host and clears the local terminal, and knows nothing of the pipeline. It goes better with Write-Host .
Since your function loops eternally, the pipeline output never finishes, so what you would get get is this endless list with one set of headings:
CommandType Name Version Source
----------- ---- ------- ------
Alias ls -> Get-ChildItem
Alias ls -> Get-ChildItem
Alias ls -> Get-ChildItem
Alias ls -> Get-ChildItem
Alias ls -> Get-ChildItem
Alias ls -> Get-ChildItem
but you clear the /display/ in the middle of the list, so it carries on printing the subsequent items without the headings.
If you explicitly write to Format-Table in your command you can get the headings repeated:
watch { Get-Alias ls | Format-Table }