Powershell gotchas: standard out breaks lines to fit console

May 14, 2012

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When Powershell writes to standard out, and there is now redirection in the Powershell script itself, it will assume that it writes to a console. Because of this, it kindly breaks lines if they are longer than 80 characters. So, given the following powershell file (.ps1):

# line-gunk.ps1
"123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890"

If you run this Powershell file from the Windows command line, and redirects output to a file:

C:>@powershell -file .line-gunk.ps1 > foo.txt

Then you will get:

1234567890123456789012345678901234567890123456789012345678901234567890123456789
01234567890

However, if you do the redirection in Powershell, it’s fine:

PS C:> .line-gunk.ps1 > bar.txt

A näive fix to this, would be to change your script to use Write-Host to explicity write the text to the console. However, I consider this a bad practice because it would restrict the usage of your script as you could not manipulate the output further if reusing the script. I found this entry on stackoverflow which provides a better solution. Going back to the original script, here is a fixed one that worked for me:

# line-gunk-fixed.ps1
$Host.UI.RawUI.BufferSize = New-Object Management.Automation.Host.Size(500, 25)
"123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890"

Notice that I used the simplifed version from the stackoverflow entry, which might not work in all circumstances.

Backstory

How did I come across this problem? I running Powershell build scripts in TeamCity and I was trying to report the build progress back to TeamCity. However, it somehow did not work. I then discovered that the status messages written by my script were broken by the line breaks, rendering them useless…