powershell error-handling try-catch exit-code

How To Get Exit Code From PowerShell Script

I'm trying to write a PowerShell script which sends a Slack notification whenever our build system in unable to push Docker images to Docker Hub. How can I detect and handle the Process exited with code 1 from the docker push command? I've tried the following, but the catch block isn't called.

try {
  docker push $dockerImage;
}catch{
  #Send error details to Slack
}

Solution

In Windows PowerShell and PowerShell (Core) up to version 7.3.x, calls to external programs (such as docker) never cause a statement-terminating error^[1] that you can trap with try / catch; similarly, stderr output from external program is (rightfully) not considered error output by PowerShell, and therefore $ErrorActionPreference = 'Stop' has no effect on it (for legacy exceptions in Windows PowerShell, see this answer).
- In PowerShell (Core) v7.4+, opt-in integration with PowerShell's error handling is available, via the $PSNativeCommandUseErrorActionPreference preference variable.
  - If you set this variable to $true, any external-program call that reports a nonzero exit code automatically triggers a PowerShell error in response (obviating the need for explicit $LASTEXITCODE -ne 0 checks), which then integrates with PowerShell's own error handling.^[2]
    That is, with the $ErrorActionPreference preference variable set to 'Stop', any external program reporting a nonzero exit code will then result in a script-terminating (fatal by default) error.
- In general, note that a statement-terminating PowerShell error (which can be caught with try / catch) does occur if PowerShell fails to even launch a command, such as when you supply a non-existent executable name or path; e.g.:
```
try   { nosuchexe foo bar }
catch { Write-Warning "Failed to invoke nosuchexe: $_" }
```
The automatic $LASTEXITCODE variable reflects the process exit code of the most recently executed external program. By convention, exit code 0 signals success, anything else an error condition.

Therefore:

docker push $dockerImage
if ($LASTEXITCODE -ne 0) {
  #Send error details to Slack
}