How can I write to standard error from PowerShell, or trap errors such that:
All these years I've survived by throwing errors or writing via Write-Error, but I'm tired and old, and in my scripts I just want to see one concise error message. I've been trying every combination of trap, throw, Write-Error, and -ErrorAction, to no avail:
try {
throw "error" # Sample code for a stack overflow. In the theater
# of your mind, imagine there is code here that does something real and useful
} catch {
Write-Error "An error occurred attempting to 'do something.' Have you tried rebooting?"
}
Here's the user experience I want to see:
C:\> & .\Do-Something.ps1
An error occurred attempting to 'do something.' Have you tried rebooting?
C:\> ▏
Instead I get:
C:\> & .\Do-Something.ps1
An error occurred attempting to 'do something.' Have you tried rebooting?
At line:1 char:1
+ Do-RealWork
+ ~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [Write-Error], WriteErrorException
+ FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException,Do-RealWork
C:\> ▏
Preface re what doesn't work:
Setting the $ErrorView preference variable $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.
While PowerShell (Core) 7+ now defaults to more concise error formatting (in the simplest case printing just the error message) via its new $ErrorView default, ConciseView, this output is only situationally single-line.
Notably, it is still multiline if the error occurs in a script (.*ps1 file) or in a function dot-sourced from a script, (including profile scripts), in which case the error message is preceded by additional lines reporting the script's file path, source-code line, and line number.
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].
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.
[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).