How can I display a 'naked' error message in PowerShell without an accompanying stacktrace?

^{Setting the automatic $ErrorView variable to 'CategoryView' causes PowerShell to output concise, single-line error representations instead, but this representation may not always include enough information, because the error message is typically not included; on the plus side, the text passed to Throw "..." is reflected, but, by contrast, Write-Error output contains no specific information while 'CategoryView' is in effect.
Adding a new error view to PowerShell that is single-line yet always contains all crucial information is being discussed for v6.}

Provided that your PowerShell code is run from a console (uses a console host), use [Console]::Error.WriteLine(), which unconditionally writes to the outside world's stderr (standard error stream):

[Console]::Error.WriteLine("An error occurred ... Have you tried rebooting?")

Note:

• This won't work from non-console hosts such as the PowerShell ISE.

• [Console]::Error.WriteLine() output doesn't print in red in the console ^[1].

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Sadly, there is no single solution that works both from within PowerShell (across hosts) and from outside of it:

• [Console]::Error.WriteLine(), while writing properly to stderr for the outside world, cannot have its output captured or suppressed inside PowerShell, and only works with the PowerShell console host.

• Similarly, $host.ui.WriteErrorLine(), even though works with all hosts, it is a UI method that works outside PowerShell's stream system as well and therefore its output too cannot be captured or suppressed in PowerShell.
  More importantly, it doesn't write to the outside world's stderr (it behaves like Write-Error in this respect, see below).

• Inside PowerShell, only Write-Error writes to PowerShell's error stream, so its output can be captured / suppressed.
  However, unfortunately, Write-Error (apart from being noisy) does not write to the outside world's stderr, unless, bizarrely, stderr is explicitly being redirected - see this answer of mine for details.

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[1] Peter (the OP himself) offers a workaround for that:

[Console]::ForegroundColor = 'red'
[Console]::Error.WriteLine("An error occurred ... Have you tried rebooting?")
[Console]::ResetColor()

suneg's helpful answer provides a function wrapper for it.

Fortunately, PowerShell automatically omits the color codes when it detects that the output is being redirected (to a file).

Building on the idea in a previous answer, you can override the built-in Write-Error cmdlet temporarily with a custom function.

# Override the built-in cmdlet with a custom version
function Write-Error($message) {
    [Console]::ForegroundColor = 'red'
    [Console]::Error.WriteLine($message)
    [Console]::ResetColor()
}

# Pretty-print "Something is wrong" on stderr (in red).
Write-Error "Something is wrong"

# Setting things back to normal 
Remove-Item function:Write-Error

# Print the standard bloated Powershell errors
Write-Error "Back to normal errors"

With this you are utilizing the fact that Powershell Functions takes precedence over cmdlets.

https://technet.microsoft.com/en-us/library/hh848304.aspx

This is the most elegant approach I've been able to come up with to both show beautiful and concise error messages, as well as letting TeamCity detect problems easily.

I needed to solve this problem myself recently so I put together a Write-ErrorMessage function as detailed here: https://intellitect.com/powershell-write-error-without-writing-stack-trace/

Specifically, I leveraged the combination

Write-Error -Message $err -ErrorAction SilentlyContinue
$Host.UI.WriteErrorLine($errorMessage)