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
}
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.
$true
, any external-program call that reports a nonzero exit code automatically triggers a PowerShell error in response (obviating the need for explicit $LASTEXITCODE -ne 0
checks), which then integrates with PowerShell's own error handling.[2]$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
}
See also:
[1] The only exception is a bug, present in Windows PowerShell and historically in PowerShell (Core) up to the no-longer-supported v7.1.x, where the combination of redirecting stderr output (2>
or *>
) with $ErrorActionPreference = 'Stop'
unexpectedly causes a script-terminating error if there's actual stderr output - see this answer.
[2] Unfortunately, as of PowerShell 7.4.x, the automatically triggered PowerShell error is a non-terminating error rather than a statement-terminating one; the latter would make more sense, as it would allow it to be selectively caught with a try
statement - see GitHub issue #18368.