PowerShell Script Starts Adding Blank Lines After 100+ Lines of Output? - powershell

Question

I seem to have encountered a weird bug, or I've missed something in my script.
In my scripts, I'm showing progress with a faux progress bar function. It works by updating the same line of the console repeatedly, mimicking a progress bar. See the function below:
# Update-Progress-Bar : v1.0 : 2013-07-29
# Displays a percentage bar. Meant to be used repeatedly to update the same console line (giving the appearance of incrementing progress).
# - $Percentage : Determines how much progress is shown on the bar.
# - $Message : The message that accompanies the progress bar.
function Update-Progress-Bar ($Percentage, $Message){
# Save the current cursor position so we can come back later.
$CursorPosition = $Host.UI.RawUI.CursorPosition
# Convert the percentage into a proper progress bar.
$ProgressBarMax = "20"
$ProgressBarCount = [Math]::Floor([Decimal]($Percentage / 5))
$ProgressBar = ("#" * $ProgressBarCount) + (" " * ($ProgressBarMax - $ProgressBarCount))
# Change the format of the percentage depending on length.
switch ($Percentage.Length){
1 {$Percentage = " " + $Percentage + "%"}
2 {$Percentage = " " + $Percentage + "%"}
default {$Percentage = $Percentage + "%"}
}
# Trim or pad the message as necessary.
$MessageMaxLength = "50"
if ($Message.Length -gt $MessageMaxLength){ $Message = $Message.Remove($MessageMaxLength) }
else { $Message = $Message + (" " * ($MessageMaxLength - $Message.Length)) }
# Display our progress bar, percentage, and message.
Write-Host -nonewline -ForeGroundColor Blue "[$ProgressBar] $Percentage"
Write-Host " | $Message"
# Revert back to the original cursor position.
$Host.UI.RawUI.CursorPosition = $CursorPosition
}
For whatever reason, after working for about 100+ records (I'm using this as part of a script where I'm regularly performing actions against 1000s of machines), it starts performing double line breaks, which ruins the functionality of the progress bar. So I end up with this...
[ 126 / 2275 ] ComputerName1
[ ] 0% | Verifying network connectivity...
[## ] 10% | Verifying file system access...
[#### ] 20% | Determining installed operating system...
[###### ] 30% | Executing action...
[####################] 100% | Action Completed
[ 127 / 2275 ] ComputerName2
[ ] 0% | Verifying network connectivity...
[## ] 10% | Verifying file system access...
[#### ] 20% | Determining installed operating system...
[###### ] 30% | Executing action...
[####################] 100% | Action Completed
When I should have....
[ 126 / 2275 ] ComputerName1
[####################] 100% | Action Completed
[ 127 / 2275 ] ComputerName2
[####################] 100% | Action Completed
Any thoughts on this issue and a possible workaround?
EDIT #1: Is it possible that this is happening when I hit the buffer height limit of the console (as in, it starts discarding the old lines of output)?
EDIT #2: I have confirmed that this issue goes away if I increase the buffer width and height of my console window. I'm still not sure how to workaround this bug though. Thoughts?

Answer 1

I verified this bug on my own machine. As soon as you start wrapping the buffer, -nonewline fails to live up to its task.
You can do a few things as a workaround:
1) Programmatically increase the BufferSize to a fixed size
$Host.UI.RawUI.BufferSize = New-Object System.Management.Automation.Host.Size(120, 5000)
2) Clear the screen every so often, perhaps every 100 nodes or after each node if you don't need to follow the output
3) Clear the screen only when you've nearly reached the buffer limit
if($Host.UI.RawUI.CursorPosition.Y -gt ($Host.UI.RawUI.BufferSize.Height - 5)) {cls}
4) Clear only old parts of the screen buffer by temporarily reducing the size of the buffer. I used your function, untouched (except renaming to remove the second "-"). With the screen buffer at 100, the odd behavior would start at number 50 (2 output lines per loop)
49 / 2000
[####################] 100% | FINAL
50 / 2000
[#### ] 20% | First
[######## ] 40% | Second
[############ ] 60% | Third
[################ ] 80% | Fourth
[####################] 100% | FINAL
51 / 2000
[#### ] 20% | First
[######## ] 40% | Second
[############ ] 60% | Third
[################ ] 80% | Fourth
[####################] 100% | FINAL
But with the BufferSize switching, I made it all the way to 2000/2000 without a hitch
1998 / 2000
[####################] 100% | FINAL
1999 / 2000
[####################] 100% | FINAL
2000 / 2000
[####################] 100% | FINAL
$range = 1..2000
Test code below:
foreach($i in $range)
{
$Host.UI.RawUI.BufferSize = New-Object System.Management.Automation.Host.Size(120, 3000)
Write-Host
Write-Host $i "/ 2000"
Update-ProgressBar "20" "First"
Update-ProgressBar "40" "Second"
Update-ProgressBar "60" "Third"
Update-ProgressBar "80" "Fourth"
Update-ProgressBar "100" "FINAL"
$Host.UI.RawUI.BufferSize = New-Object System.Management.Automation.Host.Size(120, 2990)
}
Realistically, you could combine 3 and 4 so that you only clear the old parts of the buffer when it is nearly full.