Sunday, 18 September 2011

How Powershell Behaves with Errors in the Script

PowerShell has two kinds of errors; terminating errors and non-terminating errors

Terminating errors are the errors that can stop command execution cold. Non-terminating errors provide an additional challenge, as you need to be notified of failed operations and continue with pipeline operations. Powershell by default tries to continue when non-terminating errors occur. Something I don't want to happen when I call Powershell with my CI server to release software. If there are errors I want the script to stop and tell me what is wrong - not the script to continue and report that everything went OK.

$ErrorActionPreference is a variable that describes how PowerShell will treat non-terminating errors. $ErrorActionPreference has four self-explanatory options:

  • Continue (the default)
  • SilentlyContinue
  • Inquire
  • Stop

To exit your script with an error code (if an error occurred), you'll need to exit using the $LastExitCode variable. This variable returns a number that represents the exitcode of the last script or application, needed for your CI server to know if the script ran successfully. Here's a template for what I use with the Jenkins CI server...

$ErrorActionPreference = "Stop"

# Do something...

exit $LastExitCode

Anything else?

Well, yeah... $error is an array of all the errors that have occurred in the current session up to the number specified in $MaximumErrorCount. Also, $? is a boolean value that is $true if the previous operation succeeded and $false if it did not.

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