How to tracing script flow

Question

I'm fairly new to Powershell and have written some pretty large scripts ie a script that calls others scripts which have functions nested in other functions. When I launch this script I sometimes get errors that I don't know where they came from. Is there an easy way to see where this script terminated so I can troubleshoot the error?

Answer 1

You can use Set-PsDebug to get PowerShell to output almost every line it runs:

Set-PSDebug -Trace 1;

Only downside is you'll probably end up with a lot of output to wade through...

Answer 2

For debugging to see where your error's are coming from I suggest debugging with the ISE or with PowerGUI.

You can also get a transcript of you script using the Start-Transcript cmdlet which will write all console activity to file. So you can put statements such as Write-Host "Doing XYZ" and those will show up in the transcript log.

If you catch exceptions with a try catch or use a trap you can write the line number and column of the exception like this:

$ErrorActionPreference = 'Stop'

trap {
  Write-Host "Error on line $($_.InvocationInfo.ScriptLineNumber)"
  exit 1
}

try {
    Get-Item DoesntExist
} catch {
    Write-Host ("Error occurred on line: " + $_.InvocationInfo.ScriptLineNumber)
}

$_.InvocationInfo has other details about were the error is coming from.

By setting $ErrorActionPreference = "Stop" you ensure that any error triggers the trap{} block, which in this case writes out the line the script got to and exits.